1. Recommended GitLab's own registry over Docker Hub. (Reason: https://gitlab.com/famedly/conduit/-/merge_requests/492#note_1457220261)
2. Added the development image :next to the list of options.
3. Displayed text for Docker Hub now contains "docker.io" as part of the link for easier copy-paste for podman users. Clicking on the link still takes to the website.

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.