Revise CRD code markers/validations

[pmalek]

Problem statement

5103 tries to solve #5061 but leaves the CRD validations unreviewed.

For instance:

• KongConsumer's Username is required (enforced in admission webhook) but that could easily be changed to a required field on the CRD level via:

    // +kubebuilder:validation:Required
    Username string `json:"username"`

  This unfortunately can only be done when the // +kubebuilder:validation:Optional is removed from the package as that overrides the field level setting.

Acceptance criteria

• [ ] All Kong provided CRDs are reviewed for moving validation code from admission webhook to CRD level and all possible changes are merged to main

[randmonkey]

@pmalek Please check if there are nothing in the current webhook that can be moved to CRD annotations. If there is anything to do, please move it to milestone 3.4, otherwise close it.

[pmalek]

Just did a spot check and I don't see anything obvious that could be moved to CEL/code markers.

Most of what we do in KIC's admission webhook these days is either cross object validation or validating against Gateway schema, neither of which can be done in CEL/code markers.

Closing.