Exclude "service members" from heroes list in room summary / sliding sync when state is set in room (Implement MSC4171)

[Half-Shot]

See matrix-org/matrix-spec-proposals#4171

The purpose behind the MSC is to ensure that when you add bots such as audit bots or so on to unnamed rooms, they do not show up as part of the calculated room name (or you end up with "Alice, Bob and SurpriseBot"). The bot should show up in the member list as normal, but just not prominently in the room name.

[Half-Shot]

https://github.com/Half-Shot/synapse/tree/hs/msc4171-heroes implements this, but having issues with my fork at the moment so a PR will be up later.