chore: update features gates for v3, remove Gateway feature gate

[pmalek]

What this PR does / why we need it:

This PR:

• Removes the Gateway feature gate. It was enabled by default for a while now, 3.0 is a good opportunity to remove it.
• Updates the https://github.com/Kong/kubernetes-ingress-controller/blob/main/FEATURE_GATES.md
• Moves the graduated or removed features gates from https://github.com/Kong/kubernetes-ingress-controller/blob/main/FEATURE_GATES.md#feature-gates-for-alpha-or-beta-features to https://github.com/Kong/kubernetes-ingress-controller/blob/main/FEATURE_GATES.md#feature-gates-for-graduated-or-deprecated-features

Special notes for your reviewer:

We do not have CLI flags for enabling/disabling Gateway API controllers. We only did that with the feature flags up until now hence this PR flips the enable criteria on those controllers to true, i.e. always enabled.

Do we want to introduce those?

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

All modified and coverable lines are covered by tests ✅

Comparison is base (7da78ac) 77.6% compared to head (2d5b6be) 77.7%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #4968   +/-   ##
=====================================
  Coverage   77.6%   77.7%           
=====================================
  Files        167     167           
  Lines      18708   18707    -1     
=====================================
+ Hits       14529   14540   +11     
+ Misses      3345    3337    -8     
+ Partials     834     830    -4     

Files	Coverage Δ
internal/manager/controllerdef.go	99.4% <100.0%> (ø)
internal/manager/featuregates/feature_gates.go	100.0% <ø> (ø)

... and 8 files with indirect coverage changes

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[pmalek]

@programmer04 Let's introduce the CLI flags first and adjust the test code first #4971. Then we can clean up the feature flags here.