Adding a Per ks/table dashboard

[amnonh]

This PR is currently an RFC mode, for customers that would set scylla to report per table metrics, it would allow to show per table metrics.

The user chooses a keyspace and can choose specific table for that keyspace.

To handle performance issues:

1. there are new recording rules that would generate the avarage, p95 and p99 per table latencies.
2. The per tables rows are closed by default
   

So the user can open only the relevant table

Fixes #998