Add persistence to Ray

[javiermtorres]

What's changing

A Redis container has been added to the compose definition to hold the Ray metadata.

Closes #690

How to test it

Steps to test the changes:

1. Start as usual with make local-up
2. Run the backend integration tests with make test-backend-integration
3. Check the jobs in the dashboards
4. Stop the containers with ^C
5. Restart them with make local-up
6. Check the dashboard again. The jobs information should still be visible.

Additional notes for reviewers

N/A

I already...

• Tested the changes in a working environment to ensure they work as expected
• Added some tests for any new functionality
  • N/A
• Updated the documentation (both comments in code and product documentation under /docs)
• Checked if a (backend) DB migration step was required and included it if required
  • No DB changes done

[dpoulopoulos]

Looks good to me! Thanks for this! I left a minor comment.

[dpoulopoulos]

Should we add a make target to allow the user to clean this, if they choose to?

[javiermtorres]

We have talked about using labels to prune the right containers. IIRC the volumes can get pruned too with a certain flag. I'll check open PRs to see how far we've done of this. IMO this volume should have the same life cycle as the ray and redis containers, so there should be no need to clean it up separately.