Rename `SpecialSubscription` to `CustomFilterSubscription`
This is a subtask of #421 (closed)
Background / User story
SpecialSubscription
is a bit of a misnommer and it should be renamed CustomFilterSubscription
to reflect its uses.
What to change
- Rename
SpecialSubscription
toCustomFilterSubscription
- Update tests
Hints for testing
Integration notes
- Change the name of the class in the calling code.