Update Error Message when Secret Reference is invalid

[jm96441n]

Changes proposed in this PR

• make the error message when the certificate reference kind/group is incorrect more descriptive. Previously the message was just certificate type is not supported which could point to an issue with the actual certificate itself or the reference for it. This PR expands the error message to tell the user how to correct the issue

How I've tested this PR

How I expect reviewers to test this PR

Checklist

• [X] Tests added
• [ ] CHANGELOG entry added