Questions based on Saved Questions for Druid?

Nobody has claimed this yet.

**Is your feature request related to a problem? Please describe.**

We at 7mind enjoy your feature that allows to create questions based on saved questions using the query builder for our Postges Data! Knowing how useful it is there, it's kind of a bummer to not have it for our Druid data (which is how we store most of our data)

**Describe the solution you'd like**
Questions based on Saved Questions for Druid data, in just the same way it works for Postgres (and other Datasources as well I suppose)

**Describe alternatives you've considered**
The only alternative we currently see is using native queries for somewhat nested problems, which is of course not that nice because very few people in our company can write json-queries for Druid and we want to empower everyone to be able to create their own questions and dashboards - which Metabase really does a great job at 👏

**How important is this feature to you?**
It's no dealbreaker but it's among my current TOP5 feature wishes for Metabase 🙃

The issue names Druid support for questions based on saved questions and compares it with Postgres, but gives no repository files, tests, or entry points. Start by locating the saved-question query-builder flow and Druid driver or query support; define the affected paths and acceptance checks before estimating implementation.

Written by the indexing model from the issue text.