ops: allow for multiple instances

[yanokwa]

The use of container_name means that you can't run multiple instances of Central on the same machine.

It also means you can't ever have a container called mail or service or secrets. Removing the container name solves this problem because Docker automatically prepends the folder name to the container (e.g., service becomes central_service_1). This happens with our PostgreSQL container already since it doesn't have a container_name.

• I have confirmed that you can upgrade existing installs of Central with this change and it loads just fine.
• I have confirmed that after upgrade, Enketo (which uses host-name based addressing) works by launching a preview. This is because Docker uses the service name to reach containers.
• I have confirmed that I can run multiple copies of Central on the same machine and they both load.

This isn't a must have change, so if it feels high risk, I'm open to waiting until after v1.2

[issa-tseng]

i think we might depend on these names in the docs?

[yanokwa]

@issa-tseng Good question. The docs seem to use docker-compose name and those are run in the folder where Central is installed, so you can still refer to the name (e.g., service, nginx).