Add "--database-custom-command" option to Docker helper script
Add "--database-custom-command" option to Docker helper script

This makes possible to launch the database used in the integration tests
with a set of custom commands, for example, to replicate those used in
CI.

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

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed