Remove hardcoded versions from start.jbpm webapp

Every time a new version of jBPM or RHPAM is released, we need to manually create PRs for the start.jbpm.org modules. This is error prone and it requires a whole new compilation and release cycle for the web app.

Ideally, the application would read from a YAML properties file the version matrix instead of having the versions hardcoded.

This script highlights the locations of the hardcoded versions:
https://github.com/kiegroup/start.jbpm.org/blob/main/hack/bump-versions.py

Having this version matrix externalized to a file, we can easily mount it into a Kubernetes configMap, having to only update this file when new versions of the related projects are released.

Acceptance Criteria:

• The web ap reads the required versions matrix from an external configuration file
• This file can be on classpath, but can be replaced by an external one via configuration. For example:

  java -DconfigFile=myversions.json -jar start.jbpm.jar
  

This JIRA requires JBPM-9757.