APIRule reconcile function refactoring

[strekm]

Description

Introduction of APIRule v1beta2 added complexity to main reconcile function that needs to be addressed before adding extAuth handler.

ACs:

• removed complexity from reconcile function
• make implementation easy to extend with another handler
• make reconcile function version aware

Additional info

• Configuration for immutable fields can be achieved by using CEL validation:

  // +kubebuilder:validation:XValidation:rule="self == oldSelf",message="Value is immutable"

  This might be useful to support conversion from v1beta2 to 1 without need for preserveUnknownFields.

DoD:

• Provide unit and integration tests.
  - [ ] Provide documentation.
• Verify if the solution works for both open-source Kyma and SAP BTP, Kyma runtime.
  - [ ] If you changed the resource limits, explain why it was needed.
• Verify that your contributions don't decrease code coverage. If they do, explain why this is the case.
  - [ ] Add release notes.

Attachments
part of: #939