Updated readme

[theo-dt]

Description

Updated readme to include section about troubleshooting issues with the Vertex AI Custom Code Service Agent

How has this been tested?

No need to test anything since only the README has been updated

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (make test-trigger and make test-all-components)
• I have successfully run the E2E tests
• I have updated any relevant documentation to reflect my changes
• No need to perform any tests since only README was changed

[felix-datatonic]

/gcbrun