feat: enable `require-image-signature` policy as `audit`

Package Merge Request

Package Changes

This MR will enable the require-image-signature kyverno policy by default for all bigbang deployments. The default behavior is audit. Users can optionally override this to enforce if they desire. The policy is configured to only inspect ironbank images.

Package MR

n/a

For Issue

Closes (#1777 (closed))

Closes #1777 (closed)