add_header will not override the Content-Type header set by the server,
but will instead add another header below, which is obviously not ideal.

The proposed change will instead tell nginx to set the correct value for
this header straight away.

When a user mounts a volume into the default volume path,
it uses the permissions and ownership from the host volume.
In most cases, this is 1000:1000, which it also uses on the inside.

If you don't mount a volume though (e.g., for testing), conduit cries:
“The database couldn't be loaded or created.”

This fix chowns the default db dir to remedy this.

Also run all builds on approved MRs

Conduit can start without a specific port being configured.
This adjusts the healthcheck script to tolerate that state.

Closes https://gitlab.com/famedly/conduit/-/issues/222

The nginx instance which is serving the .well-known endpoints can serve
the simple JSON replies directly from memory, instead of having them
as external files on disk.

 conduit default port 6167 and fix the docker healthcheck

And mention that an empty string can be used to configure
Conduit purely with env vars.