feat: enable ReferenceGrant controller if Gateway feature gate turned on

[randmonkey]

What this PR does / why we need it:

Since ReferenceGrant has been promoted to beta, we should enable it by default if gateway turned on.

Which issue this PR fixes:

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

Base: 74.0% // Head: 73.8% // Decreases project coverage by -0.2% ⚠️

Coverage data is based on head (4bee205) compared to base (d839f48).
Patch coverage: 100.0% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3519     +/-   ##
=======================================
- Coverage   74.0%   73.8%   -0.2%     
=======================================
  Files        116     116             
  Lines      13883   13883             
=======================================
- Hits       10277   10258     -19     
- Misses      2949    2962     +13     
- Partials     657     663      +6     

Impacted Files	Coverage Δ
internal/manager/controllerdef.go	98.7% <100.0%> (ø)
...nternal/controllers/gateway/udproute_controller.go	71.6% <0.0%> (-2.2%)	⬇️
...nternal/controllers/gateway/tlsroute_controller.go	71.4% <0.0%> (-2.1%)	⬇️
...ternal/controllers/gateway/httproute_controller.go	69.7% <0.0%> (-1.9%)	⬇️
internal/dataplane/parser/parser.go	90.7% <0.0%> (+0.6%)	⬆️

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[pmalek]

One nit but other than that 👍