Release docker images to github packages (ghcr.io)

[lmsurpre]

Is your feature request related to a problem? Please describe.
For IBM FHIR Server, we pushed our docker images to DockerHub under the organization ibmcom.

The LinuxForHealth project has its own organization on DockerHub at https://hub.docker.com/u/linuxforhealth.
However, DockerHub has some rather significant limitations for us and alternative image hosting is readily available.

I discussed it with @dixonwhitmire and we decided to use the GitHub Container Registry for our images going forward.
This will mean a longer image path (ghcr.io/linuxforhealth/fhir-server instead of just linuxforhealth/fhir-server) but we think its still reasonable.

Describe the solution you'd like
Update our automation

Question: Will github packages let us update an image thats already been pushed. We do that today to ensure that the base OS stays up-to-date with security fixes. I assume it will allow that since its pretty common practice.

Describe alternatives you've considered
Continue pushing to DockerHub (under linuxforhealth)

Acceptance Criteria

1. GIVEN [a precondition]
   AND [another precondition]
   WHEN [test step]
   AND [test step]
   THEN [verification step]
   AND [verification step]

Additional context
At least two workflows need updating:

• release.yml
• rebuild.yml

[punktilious]

Confirmed that the docker image exists:

REPOSITORY                                   TAG                                      IMAGE ID      CREATED        SIZE
ghcr.io/linuxforhealth/fhir-server           latest                                   415b2d5018c8  11 days ago    1.26 GB

Pulled it, ran it with bootstrapping enabled and was able to POST a new resource.