Feature request: Allow event type filtering for application services

[kevinrademan]

Feature
Current application services allows you to limit the events received by using regular expressions on user_ids, room_ids or room alias. If would also be very useful to also allow events to by filtered on the "type" type field.

Use case
We have several application services that uses user presence to determine the bot message/behavior (eg OfflineAgentBot). In our system this presence information is based on a group. These groups can range from 1 user to 500 users, which makes it impossible to efficiently query this information from the homeserver. Currently we're using MSC2409 feature to have presence events pushed via application service to an endpoint which then aggregates and caches group presence in redis. The problem currently is that there is a very large number of ignored events because we cannot filter on the type of event.

[kevinrademan]

Just noticed there is already an spec for this
https://github.com/matrix-org/matrix-doc/issues/1306