api: add skipBackgroundRequests support for MutatingPolicy and GeneratingPolicy

[atharrva01]

Summary

This PR adds support for skipBackgroundRequests to MutatingPolicy and
GeneratingPolicy so they behave the same way as ClusterPolicy.

What I changed

• Added an optional skipBackgroundRequests field to the evaluation
  configuration for both policy types
• Added helper methods to resolve the effective value safely, defaulting
  to true
• Regenerated CRDs, Helm charts, and API docs to include the new field

Why this change

Right now, skipBackgroundRequests is available for ClusterPolicy, but not for
MutatingPolicy or GeneratingPolicy. This makes it hard to use features like
mutateExisting or generateExisting with background requests in a consistent
way.

With this change, users can explicitly set skipBackgroundRequests: false when
they want background controller requests to be processed, while keeping the
existing default behavior unchanged.

Backward compatibility

This is fully backward compatible. Policies that don’t specify the field will
continue to skip background requests by default.

Related issue

• Support skipBackgroundRequests for MutatingPolicy and GeneratingPolicy types kyverno#14852

[atharrva01]

hi @eddycharly @JimBugwadia I’ve added skipBackgroundRequests support for MutatingPolicy and GeneratingPolicy to bring them in line with ClusterPolicy. Would appreciate a quick look when you get a chance, happy to make any adjustments.