Create a Github workflow for automated testing of agenta-cli commands

[aakrem]

Objective: Implement a GitHub Actions workflow to automate tests for agenta-cli on every PR to ensure functionality remains intact.

The workflow should be similar to the checks we already have (prettier, backend tests..) that should be triggered on each PR or pr update.

Regarding where to serve we can start with serving locally.
If it ends up being complicated or time consuming let's serve to oss.

We want to start with

agenta init
agenta variant serve -app app.py
agenta variant serve -app app.py (overwrite)

Blocked by #1609

[mmabrouk]

Closed in #1609