create secure credentials

Even a demonstrator needs some security, so the credentials in docker-compose.yml need to created at setup by random.

Definition of Done:

• extend docker-compose.bootstrap.yml write configure script to create credentials
• pass credentials to docker-compose.yml (probably through docker secrets) --> using /.env file
• pass credentials to admin --> console output on first generation and files in /.env.d/
• test
• write documentation
• announce to colleagues who run demonstrators --> it is just @ilka.schulz ...

Hints:

• none...