feat: Implement msc 3381 polls #1978

Job	Run time
dart / dart_analyzer	37s
general / conventional_commits	7s
app_jobs / e2ee_test (synapse)	1m 56s
app_jobs / coverage_without_olm	2m 11s
app_jobs / e2ee_test (dendrite)	1m 12s
app_jobs / coverage	2m 25s
app_jobs / e2ee_test (conduit)	1m 54s
app_jobs / dart_web_compatible	58s
app_jobs / database_web_tests	46s
app_jobs / pub-dev-dry-run	26s
app_jobs / merge_converage	41s
app_jobs / review_app_coverage / deploy_review_app	10s
app_jobs / review_app_coverage / cleanup_review_app	18s
app_jobs / review_app_coverage / qa_app	0s
	13m 41s

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