feat: support mergeGateways in EnvoyPatchPolicy

[cnvergence]

What type of PR is this?

feat: support mergeGateways in EnvoyPatchPolicy

What this PR does / why we need it:
Support EnvoyPatchPolicy when MergeGateways is enabled and make sure that it targets GatewayClass instead Gateway. As when mergeGateways is enabled, there will be one Envoy deployment for all Gateways in the cluster.

Which issue(s) this PR fixes:

Fixes #2308

[github-actions]

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[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (da0d0dc) 64.72% compared to head (24587c7) 64.73%.

Files	Patch %	Lines
internal/gatewayapi/envoypatchpolicy.go	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2320      +/-   ##
==========================================
+ Coverage   64.72%   64.73%   +0.01%     
==========================================
  Files         113      113              
  Lines       16442    16445       +3     
==========================================
+ Hits        10642    10646       +4     
+ Misses       5130     5129       -1     
  Partials      670      670              

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[arkodg]

@cnvergence this does make sense, can you please expand on the WHY in the PR description ?

you will also need to update the validation logic

gateway/internal/gatewayapi/envoypatchpolicy.go

Line 69 in bf8eaa4

// Ensure policy can only target a Gateway

to make sure targetRef type is KindGatewayClass when mergeGateways is true

this feature will also require some additional docs to explain this to the end user

[cnvergence]

@arkodg right, I will add this to the GatewayClass level
Also need to fix this #2308 (comment)

[cnvergence]

nvm, it works as expected

[arkodg]

LGTM thanks !

[zirain]

/retest