Add JavaScript integration tests

[niknetniko]

Inspired by the tests for Pythia, this adds "integration tests". Since we now have a set of JavaScript exercises, this will test the sample solution of all exercises (except blacklisted ones), and check that they are correct.

To prevent false failed tests, the repo is pinned to a known commit, meaning it will need to be updated manually every once in a while.

In the future, we could add other repositories if we want to ensure compatibility with existing exercises.

TODO:

• Add deploy key to js repo
• Run the test every time
• Make the test optional for merging (maybe we want this in the future?)
• Make tests stricter: at least count number of tests (checking the actual feedback is probably overkill).
• Do not use the Dodona docker image for this, use the dependencies from this repo for it.
  • Or not, maybe using it is good?