Upgrade Synapse to 1.19.1

[ulope]

Problem Description

We're still using Synapse 1.10.1.
There have been a lot of bug / security fixes since then.

Most urgently this is needed because there's a bug in applying retention policies in 1.10.1 (matrix-org/synapse#6713) which currently makes the databases grow boundlessly on our test servers.

The impact of the following changes need to be evaluated before we can perform the upgrade:

Backwards compatibility:

• EthAuthProvider:
  • registration handler async: Convert the registration handler to async/await. matrix-org/synapse#7649
  • Auth handler async / await: Convert auth handler to async/await matrix-org/synapse#7261
• Raiden Client:
  • displayname and avatar_url are no longer sent on m.room.member events if they are missing: Omit displayname or avatar_url if they aren't set instead of returning null matrix-org/synapse#7497
  • publicRooms endpoint no longer delivers aliases: Do not return aliases as part of the public room list matrix-org/synapse#6970
  • Alias semantics changes (MSC2432): Implement new alias semantics (MSC2432) matrix-org/synapse#6898

Features (can possibly improve performance and / or simplify implementations):

• Admin device API: Add device management to admin API matrix-org/synapse#7481
• Cache factor config: Allow configuration of Synapse's cache without using synctl or environment variables matrix-org/synapse#6391
• Worker replication can now use Redis: Add ability to run replication protocol over redis. matrix-org/synapse#7040
• Admin users can create room aliases without having to join it: Allow admins to create aliases when they are not in the room matrix-org/synapse#7191
• Room aliases can be deleted by canonical alias power level users: Allow deleting an alias if the user has sufficient power level matrix-org/synapse#6986

[fredo]

do we actually use the endpoint publicRooms?