Support Matrix 1.4

[clokep]

Matrix 1.4 was just released, we should break down a list of things that Synapse needs to support it. See the release notes: https://matrix.org/blog/2022/09/29/matrix-v-1-4-release#client-server-api

Depends on #13953

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Client-Server API

• Remove unused policy room sharing mechanism, as per MSC3844.
• Add a .m.rule.room.server_acl push rule to match m.room.server_acl events, as per MSC3786. Implement MSC3786: Add a default push rule to ignore m.room.server_acl events #12601, Use the stable prefix for MSC3786. #13997
• Add Cross-Origin-Resource-Policy (CORP) headers to media repository, as per MSC3828. Add Cross-Origin-Resource-Policy header to thumbnail and download media endpoints #12944
• Copy a room's type when upgrading it, as per MSC3818. Implement MSC3818: copy room type on upgrade #12786
• Add room_types filter and room_type response to /publicRooms, as per MSC3827. Implement MSC3827: Filtering of /publicRooms by room type #13031
• Add m.replace relations (event edits), as per MSC2676. Synapse does not apply edits to events other than m.room.message #12793, Synapse does not bundle m.replace aggregations for events other than m.room.message #12503
• Add m.read.private receipts, as per MSC2285.
• Make m.fully_read optional on /read_markers, as per MSC2285.
• Allow m.fully_read markers to be set from /receipts, as per MSC2285.
• Add threading via m.thread relations, as per MSC3440, MSC3816, MSC3856, and MSC3715. Add an API for listing threads in a room. #13394
• Add per-thread notifications and read receipts, as per MSC3771 and MSC3773. Notifications for threads #12550

Server-Server API

• Add per-thread notifications and read receipts, as per MSC3771 and MSC3773. Notifications for threads #12550

Application Service API

• Replace homeserver authorization approach with an Authorization header instead of access_token when talking to the application service, as per MSC2832. Send the appservice access token as a header. #13996