feat(sliding_sync): Add m.room.join_rules to the required state

[jmartinesp]

We need the join rules state event to prevent the SDK from assuming a room with an unknown (as in, not loaded) join rule is public.

• Public API changes documented in changelogs (optional)

Signed-off-by:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.90%. Comparing base (b8a61cf) to head (460c04c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4239      +/-   ##
==========================================
+ Coverage   84.87%   84.90%   +0.02%     
==========================================
  Files         274      274              
  Lines       29719    29719              
==========================================
+ Hits        25225    25233       +8     
+ Misses       4494     4486       -8     

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