[KEP 3488] Promote ValidatingAdmissionPolicy to GA

[cici37]

What would you like to be added?

This is the tracking issue of promoting Validating Admission Policy to GA: kubernetes/enhancements#3488

Listed the blocking issues/features below:

• validatingadmissionpolicystatus reports error when using spec.variables #122935

• Scalability evaluation for validatingadmissionpolicy #122918

• ValidatingAdmissionPolicy using CRDs as paramKind always fails after restarting kube-apiserver #122658

• ValidatingAdmissionPolicy: variable expression type not recognized as return type in expression that evaluates the variable #120239

• ValidatingAdmissionPolicy: spec.variables should be marked omitempty #120491

• CEL in Admission(ValidatingAdmissionPolicy): explicitly excluding resources from validatingadmissionpolicy interception #122205

Issues be aware of but should not be a GA blocker

• [Flaky] test/integration/apiserver Test_ValidatingAdmissionPolicy_UpdateParamRef #122052
• CEL ValidatingAdmissionPolicy only one validation result is displayed #115920
• ValidatingAdmissionPolicy CEL validation rules do not seem to expand __dot__ and __slash__ as written in the documentation #118230

Why is this needed?

/sig api-machinery
/triage accepted

[cici37]

FYI @jpbetz @alexzielenski @jiahuif

[sftim]

/retitle [KEP 3488] Promote ValidatingAdmissionPolicy to GA

We do like to write API kinds without inner whitespace

[jpbetz]

xref kubernetes/enhancements#3488 which being used by the release team to track this enhancement