Use `docker compose exec` rather than `docker exec -ti`

[tbroyer]

Compose has a docker compose exec command that's equivalent to docker exec -ti and frees you from having to know/guess/find the name of the container: you just use the name of the service as declared in the compose file and Compose maps it for you.

In https://help.penpot.app/technical-guide/getting-started/#create-users-using-cli, the command can thus be replaced with

docker compose exec penpot-backend python3 ./manage.py create-profile

and the note that follows regarding the exact name of the container can be removed.

[breuxi]

+1 also the documentation currently still mentions a manage.sh instead of manage.py!