Reduce the number of "untyped defs" (#12716)

changelog.d/12716.misc

mypy.ini

synapse/groups/groups_server.py

synapse/http/client.py

synapse/http/federation/matrix_federation_agent.py

synapse/http/federation/srv_resolver.py

synapse/http/federation/well_known_resolver.py

synapse/http/matrixfederationclient.py

synapse/http/request_metrics.py

synapse/storage/database.py

synapse/storage/databases/main/metrics.py

synapse/storage/databases/main/stream.py

synapse/storage/persist_events.py

synapse/storage/prepare_database.py

synapse/storage/state.py

synapse/storage/types.py