Previously we were recording enrollment status telemetry everywhere we
were calling into `enroll` and `_unenroll` from onRecipe and
`updateEnrollment`. Now we record the enrollment status telemetry from
inside `NimbusTelemetry.recordEnrollment` and
`NimbusTelemetry.recordUnenrollment`, so that the enrollment status
telemetry is recorded from *every* enrollment event, not just during
`RemoteSettingsExperimentLoader.updateRecipes()`.
To help with this, a new helper has been added, `UnenrollmentCause`,
which carries all the metadata required to unenroll from an experiment
(similar how `CheckRecipeResult` carries all the metadata for enrollment
and updating enrollment) and to submit the corresponding telemetry. Now
instead of calling `unenroll()` with a reason string, you must call it
with an object returned from one of the `UenrollmentCause` utilities.
All tests that were calling `unenroll()` with a string like
"test" or "cleanup" have been updated to remove the reason string. When
it is not present, the `UnenrollmentCause` will default to an "unknown"
reason, which is good enough for test cleanup.
Differential Revision: https://phabricator.services.mozilla.com/D243212
149d1a110f