OCPBUGS-28723: Improve Create serverless function error message

[Lucifergene]

Fixes: https://issues.redhat.com/browse/OCPBUGS-28723

Analysis / Root cause: The requirement of func.yaml was not clear and had no info about it.

Solution Description: Added a proper reason and link to explore the Func CLI.

Screen shots / Gifs for design review:

Unit test coverage report: Not changed

Test setup:

1. Install Serverless operator
2. Paste a random Git Repo URL in the Create Serverless Function Form.

Browser conformance:

• [x] Chrome
• [x] Firefox
• [ ] Safari
• [ ] Edge