Improve CI workflows

[mauricioaniche]

With the assignments on this repo, we need to update our CI scripts:

• The maven test, I'd suggest just to run a few of them in a smoke test fashion. (If we run them all, we gotta point to this repo and not to the old one anymore)
• A JUnit test that goes through all exercises and see if they get to a 100 (this should be a good proxy for the maven behavior)
• Run the different test suites (unit tests, slow CI tests, and the new JUnit test above) in parallel
• I'd suggest removing the docker tests that run unit tests
• I'd remove Selenium tests from the CI pipeline as the code isn't reflected in Weblab anyways, and this is just currently slowing down the CI.