Support group by in Snuba admin database cluster tool

[onkar]

Environment

Snuba admin

Steps to Reproduce

When someone looks into the database cluster tool, they see the view of all database clusters. There is no easy way to get just the cluster names unless the user iterates through all nodes. This experience could be improved.

Expected Result

User can do the group by through cluster tool

Actual Result

User does not have a way to do group by