Support environment identification

In order to be able to group tests by host, add a way to uniquely identify the environment by origin.

This could take the form of an origin-unique ID stored in `environment`, which shouldn't require the origin name in it, since that's already in the "test" object. However, we need to check what kind of query would that require.

Inspect how the environment and test objects are represented, along with the existing query paths. Determine a unique environment identifier by origin that does not duplicate the origin name, and confirm that environments can then be grouped by host.

Written by the indexing model from the issue text.