Bring auto-accept invite logic into Synapse #1351

Job	Run time
lint-newsfile	30s
check-lockfile	7s
changes	3s
lint-crlf	4s
check-schema-delta	37s
check-sampleconfig	40s
lint	46s
lint-clippy	0s
Typechecking	1m 24s
lint-pydantic	40s
lint-clippy-nightly	0s
lint-rustfmt	0s
linting-done	2s
calculate-test-jobs	8s
portdb (3.8, 11)	2m 58s
portdb (3.11, 15)	2m 42s
complement (monolith, SQLite)	12m 19s
cargo-test	0s
complement (monolith, Postgres)	12m 59s
trial-olddeps	6m 55s
complement (workers, Postgres)	19m 48s
trial-pypy	0s
cargo-bench	0s
sytest (focal)	8m 27s
trial (3.8, sqlite, all)	4m 23s
sytest (focal, postgres)	10m 4s
trial (3.8, postgres, 11, all)	10m 58s
sytest (focal, multi-postgres, workers)	13m 23s
trial (3.8, sqlite)	4m 16s
sytest (focal, multi-postgres, workers, asyncio)	19m 19s
export-data	2m 14s
tests-done	3s
	2h 15m 49s

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