Officially support Scylla

We basically already support running JanusGraph with Scylla but we don't communicate that anywhere. I suggest that we add Scylla to our test suite running with GitHub actions and then add it to the list of tested projects [in our changelog](https://docs.janusgraph.org/changelog/) and in the [release notes](https://github.com/JanusGraph/janusgraph/releases). Afterwards we could add a small section to the docs explaining how to use Scylla with the CQL backend.

- [x] Test Scylla automatically with GitHub actions #2351
- [x] Fix Hadoop integration tests for Scylla #2505
- [x] Document tested versions in changelog and release notes
- [x] Document how to use Scylla with the CQL backend (fixed in #3058)
- [ ] Fix SSL integration tests for Scylla #3595
- [ ] Add possibility to switch between `scylla` and `cql` dependencies in JanusGraph Server #3580

Review the checklist and the remaining issues #3595 and #3580, starting with the Scylla SSL integration tests and JanusGraph Server dependency selection. Check the GitHub Actions setup, changelog, release notes, and CQL backend documentation. Done means the remaining Scylla support tasks are resolved and its supported usage is documented.

Written by the indexing model from the issue text.