Add ScyllaDB support documentation and tests

[andrii-kysylevskyi]

Motivation
ScyllaDB is a drop-in, performance-focused replacement for Apache Cassandra. It works out of the box with FiloDB simply by replacing the Cassandra connection string with a ScyllaDB one in the extension (verified this locally)

Solution
The suggestion is to:

• Add a change to README.md and the architecture.md files
• Add new ScyllaDB tests that extend Cassandra tests, but assume a connection to the ScyllaDB docker container

Additional context / Benefits:

• For new FiloDB users, this makes it clear that they can use ScyllaDB out of the box if their organisation already runs it, without needing to rely on Cassandra directly.
• For existing FiloDB users, it highlights that they have the option to migrate from Cassandra to ScyllaDB if performance or scalability becomes a concern, knowing that FiloDB will continue to work seamlessly.

I am happy to work on those changes and will submit a PR soon

[andrii-kysylevskyi]

@vishramachandran Hi Vish! I noticed you were submitting some PR's recently, so I decided to try tagging you. Is there any chance you could take a look at the PR I have submitted for this issue whenever you have some time?
If you cannot work on this, could you please suggest someone else?

Thanks a lot in advance!