Refactor creation of publisher docker image

[liberaliscomputing]

We need to refactor the creation of a publisher Docker image because:

• The upstream repository doesn't curate tools.json anymore where we used to parse target version information, which, in turn, is used by scripts/fetch_publisher_jar.sh to pull a specific version of a publisher CLI from https://oss.sonatype.org.
• HL7 curates every release at https://github.com/HL7/fhir-ig-publisher/releases and the latest release is located at https://github.com/HL7/fhir-ig-publisher/releases/latest/download/publisher.jar