Add check for annotations field while looking for pkg_repo_ann

[praveenrewar]

What this PR does / why we need it:

Add check for annotations field while looking for pkg_repo_ann

Manually tested the following scenarios:

• Existing package with no annotation present (package repository was successfully created and assumed ownership of the package)
• Existing package with some annotations present (package repository was successfully created and assumed ownership of the package)
• Existing package part of another repository (package repository was created successfully without owning the package)

Which issue(s) this PR fixes:

Fixes #1054

Does this PR introduce a user-facing change?

Additional Notes for your reviewer:

Review Checklist:

• Follows the developer guidelines
• Relevant tests are added or updated
• Relevant docs in this repo added or updated
• Relevant carvel.dev docs added or updated in a separate PR and there's
  a link to that PR
• Code is at least as readable and maintainable as it was before this
  change

Additional documentation e.g., Proposal, usage docs, etc.:

[neil-hickey]

LGTM - I would really like it if there was a test for this. I saw you did manual testing... Given urgency, happy to merge. But I think if we can - we should have test for it

[praveenrewar]

We have tests for scenarios that cover overlapping packages from 2 different package repositories. I have added a test to cover a scenario where the existing package is not part of any repository.

[neil-hickey]

LGTM, ty for adding the test!