Fix backfilling

[S7evinK]

This should fix two issues with backfilling:

1. right after creating and joining a room over federation, we are doing a /backfill request, which would return redacted events, because the authEvents are empty. Even though the spec states that, in the absence of a history visibility event, it should be handled as shared.
2. gomatrixserverlib: unsupported room version '' - because, well, we were never setting the roomInfo field..

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (d13466c) 65.64% compared to head (11fed6e) 65.64%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3117   +/-   ##
=======================================
  Coverage   65.64%   65.64%           
=======================================
  Files         502      502           
  Lines       55198    55192    -6     
=======================================
- Hits        36234    36232    -2     
+ Misses      15221    15220    -1     
+ Partials     3743     3740    -3     

Flag	Coverage Δ
unittests	49.69% <0.00%> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
roomserver/auth/auth.go	88.00% <ø> (-0.89%)	⬇️
roomserver/internal/perform/perform_backfill.go	49.78% <0.00%> (-1.08%)	⬇️

... and 9 files with indirect coverage changes

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