[chore] Fix enablement variable setting priority

[ccfishk]

What this PR does / why we need it:
KIC starts a controller only CRD exists on the cluster though user off the CR plugin through enablement environment variable.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #
Enablement environment variable flag exposed user (i.e --controller-kongclusterplugin, --controller-knativeingress)should have highest priority.

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Merging #1578 (20f7acd) into next (208733f) will decrease coverage by 11.73%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##             next    #1578       +/-   ##
===========================================
- Coverage   51.51%   39.78%   -11.74%     
===========================================
  Files          93       91        -2     
  Lines        8737     8327      -410     
===========================================
- Hits         4501     3313     -1188     
- Misses       3926     4842      +916     
+ Partials      310      172      -138     

Flag	Coverage Δ
integration-test	?
unit-test	39.78% <0.00%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
railgun/internal/ctrlutils/ingress-status.go	0.00% <ø> (-66.00%)	⬇️
railgun/internal/manager/controllerdef.go	0.00% <0.00%> (-88.49%)	⬇️
railgun/internal/manager/run.go	0.00% <0.00%> (-50.00%)	⬇️
railgun/internal/manager/ingressapi.go	0.00% <0.00%> (-97.06%)	⬇️
railgun/internal/ctrlutils/utils.go	0.00% <0.00%> (-93.75%)	⬇️
railgun/internal/manager/setup.go	0.00% <0.00%> (-66.28%)	⬇️
railgun/internal/diagnostics/server.go	0.00% <0.00%> (-61.54%)	⬇️
railgun/internal/mgrutils/reports.go	0.00% <0.00%> (-55.56%)	⬇️
... and 16 more

---

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[github-actions]

Licenses differ between commit 18cc5df89a4bac4af012f7de543c8d571335ed71 and base:

+++ pr_licenses.csv	2021-07-22 16:51:57.083562640 +0000
@@ -1,3 +1,8 @@
+github.com/Masterminds/goutils,https:/Masterminds/goutils/blob/master/LICENSE.txt,Apache-2.0
+github.com/Masterminds/semver,https:/Masterminds/semver/blob/master/LICENSE.txt,MIT
+github.com/Masterminds/sprig,https:/Masterminds/sprig/blob/master/LICENSE.txt,MIT
+github.com/alecthomas/template,https:/alecthomas/template/blob/master/LICENSE,BSD-3-Clause
+github.com/alecthomas/units,https:/alecthomas/units/blob/master/COPYING,MIT
 github.com/beorn7/perks/quantile,https:/beorn7/perks/blob/master/quantile/LICENSE,MIT
 github.com/blang/semver/v4,https:/blang/semver/blob/master/v4/LICENSE,MIT
 github.com/bombsimon/logrusr,https:/bombsimon/logrusr/blob/master/LICENCE,MIT
@@ -7,6 +12,7 @@
 github.com/eapache/channels,https:/eapache/channels/blob/master/LICENSE,MIT
 github.com/eapache/queue,https:/eapache/queue/blob/master/LICENSE,MIT
 github.com/evanphx/json-patch,https:/evanphx/json-patch/blob/master/LICENSE,BSD-3-Clause
+github.com/evanphx/json-patch/v5,https:/evanphx/json-patch/blob/master/v5/LICENSE,BSD-3-Clause
 github.com/fatih/color,https:/fatih/color/blob/master/LICENSE.md,MIT
 github.com/fsnotify/fsnotify,https:/fsnotify/fsnotify/blob/master/LICENSE,BSD-3-Clause
 github.com/ghodss/yaml,https:/ghodss/yaml/blob/master/LICENSE,MIT
@@ -25,16 +31,19 @@
 github.com/hashicorp/golang-lru,https:/hashicorp/golang-lru/blob/master/LICENSE,MPL-2.0
 github.com/hashicorp/hcl,https:/hashicorp/hcl/blob/master/LICENSE,MPL-2.0
 github.com/hexops/gotextdiff,https:/hexops/gotextdiff/blob/master/LICENSE,BSD-3-Clause
+github.com/huandu/xstrings,https:/huandu/xstrings/blob/master/LICENSE,MIT
 github.com/imdario/mergo,https:/imdario/mergo/blob/master/LICENSE,BSD-3-Clause
 github.com/json-iterator/go,https:/json-iterator/go/blob/master/LICENSE,MIT
 github.com/magiconair/properties,https:/magiconair/properties/blob/master/LICENSE.md,BSD-2-Clause
 github.com/mattn/go-colorable,https:/mattn/go-colorable/blob/master/LICENSE,MIT
 github.com/mattn/go-isatty,https:/mattn/go-isatty/blob/master/LICENSE,MIT
 github.com/matttproud/golang_protobuf_extensions/pbutil,https:/matttproud/golang_protobuf_extensions/blob/master/pbutil/LICENSE,Apache-2.0
+github.com/mitchellh/copystructure,https:/mitchellh/copystructure/blob/master/LICENSE,MIT
 github.com/mitchellh/mapstructure,https:/mitchellh/mapstructure/blob/master/LICENSE,MIT
+github.com/mitchellh/reflectwalk,https:/mitchellh/reflectwalk/blob/master/LICENSE,MIT
 github.com/modern-go/concurrent,https:/modern-go/concurrent/blob/master/LICENSE,Apache-2.0
 github.com/modern-go/reflect2,https:/modern-go/reflect2/blob/master/LICENSE,Apache-2.0
-github.com/pelletier/go-toml,https:/pelletier/go-toml/blob/master/LICENSE,MIT
+github.com/pelletier/go-toml,https:/pelletier/go-toml/blob/master/LICENSE,Apache-2.0
 github.com/pkg/errors,https:/pkg/errors/blob/master/LICENSE,BSD-2-Clause
 github.com/prometheus/client_golang/prometheus,https:/prometheus/client_golang/blob/master/prometheus/LICENSE,Apache-2.0
 github.com/prometheus/client_model/go,https:/prometheus/client_model/blob/master/go/LICENSE,Apache-2.0
@@ -64,7 +73,7 @@
 go.uber.org/zap,Unknown,MIT
 gomodules.xyz/jsonpatch/v2,Unknown,Apache-2.0
 google.golang.org/protobuf,Unknown,BSD-3-Clause
-gopkg.in/evanphx/json-patch.v4,Unknown,BSD-3-Clause
+gopkg.in/alecthomas/kingpin.v2,Unknown,MIT
 gopkg.in/go-playground/pool.v3,Unknown,MIT
 gopkg.in/inf.v0,Unknown,BSD-3-Clause
 gopkg.in/ini.v1,Unknown,Apache-2.0
@@ -82,5 +91,5 @@
 knative.dev/networking/pkg,Unknown,Apache-2.0
 knative.dev/pkg,Unknown,Apache-2.0
 sigs.k8s.io/controller-runtime,Unknown,Apache-2.0
-sigs.k8s.io/structured-merge-diff/v4/value,Unknown,Apache-2.0
+sigs.k8s.io/structured-merge-diff/v4,Unknown,Apache-2.0
 sigs.k8s.io/yaml,Unknown,MIT```

[shaneutt]

I think that reducing log noise when controllers are specifically disabled is overall good, so I have no blockers for this change.

I do however have several comments, and before this PR is merged I would ask that each gets resolved, either by:

1. merging the provided suggestion
2. creating a follow up

Before KIC 2.0 releases we need to harden how this stuff works, and improve the documentation so that we're consistent and so contributors and end-users don't get confused.

[shaneutt]

In retrospect, I created a follow up item anyway because we're going to need it in any case:

#1580

While all the suggestions I made I feel are still valid, given this follow up item if you're feeling crunched for time please feel free to merge with OR without them at your discretion.