chore: Add e2e test for CS user auth flow

What does this merge request do and why?

Add a CI job to test the User JWT + Code Completions flow in a functional/integration fashion.

How to set up and validate locally

It adds a CI job, so it should be self-tested by having a green pipeline.

However, we should also test the changes to auth logic (our new bypass header).
For a simple local test, I did:

1. [Stage 1][With ENV var NOT set] Make sure AIGW_AUTH__ALLOW_BYPASS_EXTERNAL_HEADER=false in .env
2. Restart the server
3. Run curl --url 'http://localhost:5052/docs'
4. You should get {"error":"No authorization header presented"}%
5. Run curl --url 'http://localhost:5052/docs' --header 'Bypass-Auth: true'
6. You should still get {"error":"No authorization header presented"}% because we didn't set the ENV var
7. [Stage 2][With ENV var set] Make sure AIGW_AUTH__ALLOW_BYPASS_EXTERNAL_HEADER=true in .env
8. Restart the server
9. Run curl --url 'http://localhost:5052/docs'
10. You should get {"error":"No authorization header presented"}% because even though env var is set, the header is not supplied
11. Run curl --url 'http://localhost:5052/docs' --header 'Bypass-Auth: true'
12. Only in that case, env var + header, you should get 200 response

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Closes #503 (closed)