Introduce a new stream for the appservice consumer

[S7evinK]

This introduces a new stream the syncAPI produces to once it processed a OutputRoomEvent and the appservices consumes.
This is to work around a race condition where appservices receive an event before the syncAPI has handled it, this can result in e.g. calls to /joined_members returning a wrong membership list.

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (fd11e65) 65.82% compared to head (c08df16) 65.42%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
appservice/consumers/roomserver.go	62.50%	2 Missing and 1 partial ⚠️
syncapi/consumers/roomserver.go	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3277      +/-   ##
==========================================
- Coverage   65.82%   65.42%   -0.40%     
==========================================
  Files         508      509       +1     
  Lines       57392    57566     +174     
==========================================
- Hits        37776    37663     -113     
- Misses      15803    16046     +243     
- Partials     3813     3857      +44     

Flag	Coverage Δ
unittests	49.75% <75.00%> (+0.04%)	⬆️

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