Make it possible to join pseudo ID rooms

[S7evinK]

This should allow us to join pseudo ID rooms over federation.
Also needs matrix-org/gomatrixserverlib#397

[codecov]

Codecov Report

Patch coverage: 31.37% and project coverage change: -0.03 ⚠️

Comparison is base (a33ef5b) 65.48% compared to head (871d820) 65.45%.

Additional details and impacted files

@@                   Coverage Diff                   @@
##           s7evink/mxidmapping    #3119      +/-   ##
=======================================================
- Coverage                65.48%   65.45%   -0.03%     
=======================================================
  Files                      504      504              
  Lines                    56021    56201     +180     
=======================================================
+ Hits                     36685    36789     +104     
- Misses                   15547    15628      +81     
+ Partials                  3789     3784       -5     

Flag	Coverage Δ
unittests	49.76% <31.37%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
federationapi/internal/perform.go	39.92% <0.00%> (-0.82%)	⬇️
federationapi/routing/join.go	44.83% <0.00%> (-7.03%)	⬇️
roomserver/api/api.go	100.00% <ø> (ø)
roomserver/internal/api.go	76.77% <0.00%> (-3.43%)	⬇️
roomserver/internal/perform/perform_backfill.go	50.43% <0.00%> (-0.22%)	⬇️
roomserver/internal/perform/perform_create_room.go	51.29% <0.00%> (ø)
roomserver/internal/perform/perform_join.go	71.47% <0.00%> (ø)
syncapi/streams/stream_pdu.go	67.81% <15.00%> (-1.94%)	⬇️
roomserver/storage/shared/storage.go	67.93% <60.46%> (+0.53%)	⬆️
roomserver/internal/input/input_events.go	57.65% <100.00%> (+0.46%)	⬆️
... and 1 more

... and 11 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.