Couple Redash and .com (or staging)

Our dear friends of the product team would like some stats, like the number of users/groups/projects at a certain time. This is now supplied by abusing gitlab-monitor and scraping that data with prometheus.

This is wrong because:

1. Count queries are expensive!
2. We scrape it about 24 times a day, no need for such precise data
3. Prometheus removes data after 30 days, which we don't want for business stats
4. Production metrics and business metrics should be separated.

Given my points above, IMO we should connect .com and Redash. We need some form of federation over the queries though, which should be approved by 1 or 2 people with knowledge of the impact of the queries on the DB and for the privacy of our users.

What are the thoughts on this?

/cc @victorwu @regisF @briann