Replace magic numbers by named constants
Replace magic numbers by named constants

This also fixes the additional message in group rooms, as it was shown
only for the owner, but not for moderators due to a wrong
"participantType" value.

Signed-off-by: Daniel Calviño Sánchez <bd7629e975cc0e00ea7cda4ab6a120f2ee42ac1b@gmail.com>

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed