fix: run basic credentials validation despite relation with consumers

[czeslavo]

What this PR does / why we need it:

Runs credsvalidation.ValidateCredentials just after ensuring the Secret has the kongCredType key. It will make the admission webhook validate credentials' Secrets' schema even if they're not associated with any KongConsumer yet.

Which issue this PR fixes:

Fix for #4885.

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

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (a93d720) 77.7% compared to head (2c5a5f6) 77.7%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4887     +/-   ##
=======================================
- Coverage   77.7%   77.7%   -0.1%     
=======================================
  Files        164     164             
  Lines      18443   18459     +16     
=======================================
+ Hits       14340   14346      +6     
- Misses      3283    3290      +7     
- Partials     820     823      +3     

Files	Coverage Δ
internal/admission/handler.go	59.5% <100.0%> (-1.7%)	⬇️
internal/admission/validator.go	73.5% <71.4%> (-1.5%)	⬇️

... and 8 files with indirect coverage changes

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[pmalek]

Since 2.12 is an LTS and this change targets 3.0 I believe this is worth back porting to 2.12.

[pmalek]

If I understand this correctly, this might have a small performance penalty due to validating more secrets (which is sort of an obvious cost for the validation) right?

Until we remove the old way - field - (which was deprecated now in favor of a label - introduced in #4825 - which should make it more efficient (checking only those with a label

[github-actions]

The backport to release/2.12.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/2.12.x release/2.12.x
# Navigate to the new working tree
cd .worktrees/backport-release/2.12.x
# Create a new branch
git switch --create backport-4887-to-release/2.12.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 f7361dae5b5322501477715826cfc292ce02cf14
# Push it to GitHub
git push --set-upstream origin backport-4887-to-release/2.12.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/2.12.x

Then, create a pull request where the base branch is release/2.12.x and the compare/head branch is backport-4887-to-release/2.12.x.

[pmalek]

@czeslavo Note that since this PR has a changelog entry the backport failed 😢