[DINSIC] Config option to prevent showing non-fed rooms in fed /publicRooms

[anoadragon453]

Adds a config option to prevent showing rooms that have m.federate set to False from showing in the federation request to /publicRooms. By default not changing the config does not change any behaviour.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (dinsic@2712a9e). Click here to learn what that means.
The diff coverage is 61.53%.

@@            Coverage Diff            @@
##             dinsic    #4714   +/-   ##
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  Coverage          ?   72.09%           
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  Files             ?      335           
  Lines             ?    34026           
  Branches          ?        0           
=========================================
  Hits              ?    24531           
  Misses            ?     9495           
  Partials          ?        0

Impacted Files	Coverage Δ
synapse/groups/groups_server.py	77.48% <ø> (ø)
synapse/federation/transport/server.py	70.51% <ø> (ø)
synapse/config/room_directory.py	81.81% <100%> (ø)
synapse/handlers/room_list.py	75.49% <58.33%> (ø)

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