Add Babamul alert broker DataService

[DKilkenny]

Adds a DataService for Babamul, the public service of the BOOM alert broker for ZTF and LSST alerts.

Supports cone search and lookup by object id. Photometry is read from the object endpoint, which carries the full light curve: detections are stored as brightness and prv_nondetections as limits.

The API key is read from DATA_SERVICES, following the TNS pattern.

Refs issue #1405

[DKilkenny]

I have two questions:

1. Every detection I'm seeing carries isdiffpos: false and I'm currently ingesting all of them. The way I understand it is that a negative subtraction usually gets excluded from a light curve, so if that's the convention, I should be filtering them out.
2. How much enrichment do you want surfaced? Right now the only extra I save is survey since it decides which endpoint a later photometry update queries. I noticed the services here have two approaches.

• ALeRCE stores every field that isn't on the Target model
• MPC, NED, Simbad and TNS store nothing at all
  The object record has a lot available if you want it including ACAI and BTSbot classification scores and boolean flags. I chose the ZTF option for now, but I'm happy to implement the ALeRCE pattern instead.

[Fingel]

I tested this locally. Searching by name works, ra/dec works, saving the query works and creating targets. Looks good to me!

[DKilkenny]

I was checking on this PR, and I noticed a couple of tests that ran exactly the same ingest or query and just checked different parts so I consolidated them. Also, the duplicate detection test was already covered because the detection count fails when the dedup is removed.

If there's anything else I can do to help merge this PR in, happy to do so!