* commit 'f496d2587':
Incorporate review
Factor out an _AsyncEventContextImpl (#6298)
Update synapse/storage/data_stores/main/schema/delta/56/event_labels.sql
Add more data to the event_labels table and fix the indexes
Add unstable feature flag
Lint
Incorporate review
Lint
Changelog
Add integration tests for /messages
Add more integration testing
Add integration tests for sync
Add unit tests
Add index on label
Implement filtering
Store labels for new events
Add database table for keeping track of labels on events
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