Summary

New data sources are always added to the default group automatically.
This violates the principle of least privilege, as all users belong to the default group and immediately gain access to every new data source.

This issue was raised in #5015 and #5735, and a reviewer suggested controlling the behavior with an environment variable (#5735 review comment):

Let's control this with an environment variable so that the existing behaviour is still the default, but admins can modify it.

Proposal

Add a new environment variable REDASH_DATASOURCE_AUTO_ASSIGN_GROUP to control which group new data sources are assigned to.

The default value would be default to preserve backward compatibility.