Automate pushing fluree/server Docker image to Docker Hub in CI/CD pipeline

[cap10morgan]

When a new commits land on the main branch, we should build and push Docker images to Docker Hub for latest, main, and the long git sha of the HEAD commit in our GitHub Actions CI/CD pipeline.

make docker-push does latest and git sha, so we'd want to add in the branch name if we use that here (and we probably should).

We should also push release tags when there is a git tag of the format ^v(\d+\.\d+\.\d+(?:-.+)?)$. The Docker tag should be the contents of the capture group in the regex (i.e. everything except the leading v).

At some point, possibly when we implement this ticket, we should change latest to only be pushed for the latest release tag, not the latest main HEAD. That's mostly a question of when server is ready for that shift.