Filter secret names for registry pod's sa

[hasbro17]

Description of the change:
During the registry server sync the image pull secrets from the catalogsource's spec.secrets are passed
unfiltered to the serviceaccount for the registry pod.

apiVersion: operators.coreos.com/v1alpha1
kind: CatalogSource
metadata:
  name: ditto-index
  namespace: default
spec:
  sourceType: grpc
  image: quay.io/haseeb_tariq/index-image:ditto-index-0.1
  secrets:
    - ""

Passing an empty string in the secrets list breaks serverside apply for the registry pod which gets created without the metadata.managedFields when it has an empty element in the imagePullSecrets list:

kind: Pod
apiVersion: v1
metadata:
  generateName: ditto-index-
  ...
  # No managedFields on resource
spec:
  imagePullSecrets:
    - {}
    - name: ditto-index-dockercfg-djmz7
...

This prevents the registry pod from being promoted via the SSA client when
there is an update to the index image:

    couldn't ensure registry server - error ensuring updated catalog source pod:
    : detected imageID change: error during update: failed to create manager for
    existing fields: failed to convert new object (/v1, Kind=Pod) to smd typed:
    .spec.imagePullSecrets: element 0: associative list with keys has an element
    that omits key field "name" (and doesn't have default value)

To fix this, the image pull secrets list is filtered for empty strings
before being set on the serviceaccount.

Motivation for the change:
Fix for: https://bugzilla.redhat.com/show_bug.cgi?id=1945548

Similar to kubernetes-sigs/structured-merge-diff#130

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /doc
• Commit messages sensible and descriptive

[joelanford]

/lgtm

Kudos on the description as well! Super helpful!

[kevinrizza]

/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hasbro17, kevinrizza

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