Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1682
Previously, when matrix-postgres was disabled, we were setting
`matrix_mautrix_twitter_database_engine` to an invalid empty value.
Now, we always hardcode `matrix_mautrix_twitter_database_engine: postgres`,
but set/unset the database hostname and password values instead.
Updates based off the variable names used in mautrix-facebook role.
Also update port number in defauts/main.yml, and disable presence
checking, because Twitter doesn't support that.
3hhh