Allow to vary enrollment query type per-experiment

[ncalexan]

I have the following unusual situation: I want some notion of a "sub-application". Let me explain. Firefox Background Task experiments appear to Experimenter like Firefox Desktop, and by and large, this is what is desired. But enrollment into a Backround Task Messaging experiment should be determined from a different location (glean-events enrollment query type, querying the firefox_desktop_background_update Glean application). I anticipate many such Messaging experiments -- more than, say, 5 -- that make investing into supporting this in the UI reasonable.

I don't want to declare a new Experimenter application and Jetstream platform because the analysis details are (mostly) shared with the firefox_desktop platform, i.e., they're about subsequent behaviour in the Desktop browser proper.

What I would like is to be able to configure the experiment itself to in some way control the enrollment query type, and to have some details of the experiment (its slug and branch details, for example) available. Maybe that's a new enrollment query type in mozanalysis (siblings around here) and some way to reference it in Jetstream (somewhere around here). That would let me generate a query against Glean event data that produces enrolled legacy Telemetry client IDs ready for Desktop analysis.

Feedback and guidance gratefully accepted.

┆Issue is synchronized with this Jira Task

[scholtzan]

I'll put it on the agenda to discuss with the team for next year. As Jetstream and mozanalysis are set up now, this use case is not supported but adding support for it feels reasonable.