bug fixes and secret copying

[Diaphteiros]

What this PR does / why we need it:
Fixes some bugs with CRD generation and adds the possibility to propagate secrets from the provider namespace onto the target cluster.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:
This PR contains a patch release.

Release note:

Fixed some bugs related to the validation of the `DNSServiceConfig` CRD.

Fixed a bug where the `HelmRelease` manifest was generated incorrectly if a helm chart in an OCI registry was referenced.

The structure of the `DNSServiceConfig` CRD changed slightly: `spec.secretsToCopy` was an array before, now it is a struct with the `toPlatformCluster` and `toTargetCluster` fields that contain the array which was on the top-level field before.

In addition to copying secrets from the provider namespace (on the platform cluster) into the cluster namespace (also on the platform cluster), it is now also possible to copy secrets into the namespace on the target cluster where the external-dns helm chart is deployed into.