Bring auto-accept invite logic into Synapse #1151

Job	Run time
changes	2s
check-lockfile	7s
lint-crlf	7s
lint-newsfile	33s
check-sampleconfig	48s
check-schema-delta	38s
lint	54s
Typechecking	1m 36s
lint-pydantic	49s
lint-clippy	0s
lint-clippy-nightly	0s
lint-rustfmt	0s
linting-done	1s
calculate-test-jobs	10s
trial-olddeps	7m 28s
portdb (3.8, 11)	3m 8s
portdb (3.11, 15)	2m 57s
complement (monolith, SQLite)	12m 48s
cargo-test	0s
complement (monolith, Postgres)	12m 57s
complement (workers, Postgres)	20m 43s
trial-pypy	0s
cargo-bench	0s
trial (3.8, sqlite, all)	4m 30s
sytest (focal)	8m 40s
trial (3.8, postgres, 11, all)	10m 10s
sytest (focal, postgres)	9m 57s
trial (3.8, sqlite)	3m 54s
sytest (focal, multi-postgres, workers)	14m 0s
sytest (focal, multi-postgres, workers, asyncio)	2h 24m 26s
export-data	2m 16s
tests-done	2s
	4h 23m 41s

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