Define source of truth for ValidatingAdmissionPolicy objects and implement automation to keep it synced across dependents

[pmalek]

Problem statement

#1007 and Kong/charts#1215 add first ValidatingAdmissionPolicy objects that are used to validate DataPlane objects. These were added as part of #949 due to limited cost allocation for CEL expressions on CRDs.

Ideally, we would not like to keep these in multiple places and this is what this issue aims to solve.

Discussed in https://kongstrong.slack.com/archives/C011RQPHDC7/p1736959907181309

Proposed solution

Move the added ValidatingAdmissionPolicy objects definitions to https://github.com/Kong/kubernetes-configuration under e.g. config/gateway-operator/validation and add an automation which will sync this with gateway-operator chart (in the location where these objects will land after Kong/charts#1215 merges).

[czeslavo]

If we implement solution C from #770, we may leave the ValidatingAdmissionPolicy in KGO and treat it as a source of truth.