[Harmony] Bug 2005381: Clean up docker configs, run tests locally easier

[justdave]

Details

• Cleaned some of the scripts related to docker builds, got the same "does docker exist?" sanity code in all of them now.
• Converted the Release Tests GitHub Action to use a Docker image instead of running scripts directly on a GitHub test runner.
• Moved the Release Tests action into the ci.yml file and removed releases.yml (getting all of the tests listed in the same place, since they all run on the same push/branch criteria anyway.
• Added a script you can run with sh docker/run-tests-in-docker.sh which lets you pick a test to run and runs it locally.

Additional info

• bug#2005381

[dannycolin]

It works as expected.

As a follow-up bug, I'd suggest running shellcheck and aligning the code style either on POSIX sh or Bash instead of having a mixed style.

[justdave]

Note that the 6 pending checks are pending because they're listed as required for the branch and they don't exist to run them anymore because I renamed them. I can't fix it until this PR lands though, so we'll have to override the test pass requirement to land this, and then I can go fix it.