Can't set cluster private registry password in UI

[gaktive]

Internal reference: SURE-4978 Reported in 2.6.4 & 2.6.6

Issue description: If you edit a downstream cluster from the UI to add a private registry, the password provided does not apply. The same problem happens if you Edit Config > Edit as YAML. The UI or editing as YAML should allow you to enter a password and have it work.

Business impact: After upgrading, the user's images from private registries were not able to be pulled causing errors in the workloads of their downstream clusters.

Repro steps:

1. Create a custom downstream cluster
2. From cluster management edit config for the cluster
3. In the Private Registry section, check enabled and add docker.io as the default
4. Cluster will update. Then Edit as YAML
5. Add another private registry so it looks like this:

  private_registries:
    - ecr_credential_plugin: {}
      is_default: true
      url: docker.io
    - ecr_credential_plugin: {}
      is_default: false
      url: sample.domain.name.tld
      user: [email protected]
      password: <PASSWORD>

6. Save and the cluster doesn't seem to update
7. Try to create a workload that comes from the private registry added in step 5 -- the image won't pull
8. Go back to the cluster config and try to enter the password in the "Private Registry" section -- it won't apply and workloads still can't pull images from the private registry
9. Edit the cluster with kubectl edit clusters.management.cattle.io c-XXXXX -- the cluster updates and then you can pull images from the private registry
10. Interestingly, if you now change the password in the UI to a wrong password the cluster updates and the images stop pulling again. I'm not sure why this would cause an update but step 5 and 8 did not

Workaround: Edit the CRD for the cluster, see step 9 above

Actual behavior: The cluster private registry password is not applied from GUI / YAML

Expected behavior: The cluster private registry password should be applied GUI / YAML

Additional notes: This worked in 2.5.11