/api/_version_/fleet/hosts to return bad request instead of server error when passing invalid mdm_enrollment_status (#11242)

#10880

I was not able to reproduce other 500s in `/api/_version_/fleet/hosts`
other than the one fixed in the PR.

- [X] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- ~[ ] Documented any API changes (docs/Using-Fleet/REST-API.md or
docs/Contributing/API-for-contributors.md)~
- ~[ ] Documented any permissions changes~
- ~[ ] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements)~
- ~[ ] Added support on fleet's osquery simulator `cmd/osquery-perf` for
new osquery data ingestion features.~
- [X] Added/updated tests
- [X] Manual QA for all new/changed functionality
  - ~For Orbit and Fleet Desktop changes:~
- ~[ ] Manual QA must be performed in the three main OSs, macOS, Windows
and Linux.~
- ~[ ] Auto-update manual QA, from released version of component to new
version (see [tools/tuf/test](../tools/tuf/test/README.md)).~

changes/10880-api-fleet-hosts-cleanup

@@ -0,0 +1 @@
+* Fix a HTTP 500 on `GET /api/_version_/fleet/hosts` returned when `mdm_enrollment_status` is invalid.