ci jobs for slow server tests

[cmdoret]

Server tests require deploying services and are slower. Currently, CI only runs (fast) client tests, while server tests are marked as "slow" and must be run using pytest --runslow. When do we want to run the slow jobs in CI?

Objective: define CI conditions and job to run server tests.

Requirements:

• identify conditions (e.g. server files change, commits on main, PR open, ...)
• implement GA workflow
• optional: makefile rule for server tests