The problem is that when a fresh DB starts up, migrations are applied (c.f. docker-compose.yaml), but it is still required to call gargantext init.

We have to differentiate the use cases:

1. dev/prod instances don't use docker. As such the migrations are still applied by hand. gargantext init is not needed, because, apart from the system user, it also creates test users user1, user2, ...
2. developers do use docker-compose. They also don't need much the gargantext init functionality because almost always they want those test users.

What I propose is this:

1. add another migration to docker-compose which will create master and test users
2. remove gargantext init
3. add gargantext user create-admin to explicitly create the system user (and not other users)
4. optionally add gargantext user create to create users with given passwords from command line