The answer to these is: it's good to have them in both places.
The role defines the obvious things it depends on (not knowing
what setup it will find itself into), and then
`group_vars/matrix_servers` "extends" it based on everything else it
knows (the homeserver being Synapse, whether or not the internal
Postgres server is being used, etc.)
}] if (matrix_mautrix_hangouts_enabled and matrix_mautrix_hangouts_database_engine == 'postgres' and matrix_mautrix_hangouts_database_hostname == 'matrix-postgres') else [])
}] if (matrix_mautrix_signal_enabled and matrix_mautrix_signal_database_engine == 'postgres' and matrix_mautrix_signal_database_hostname == 'matrix-postgres') else [])