feat: Allow overriding namespace + make default namespace fully qualified

[srid]

PR description

• The user can now set namespace for the processes under each service
• Default namespace is now ${service}.${name} (previously, just ${name})

Tasks

• [x] Do this for postgres, to begin with.
• [x] Rest of the services

After the user overrides it:

After the user overrides the local processes as well:

[srid]

The other thing we can do here is to support a special service name, "default". Handy for cases where you run exactly 1 service, so both default namespace and the process name can drop it. Instead of db-init, it would just be postgres-init.

EDIT: Could happen in separate PR.

[srid]

To be squash merged.