Add ecmr-datamodel dependency to ecmr-backend

Related issues

"Closes #24 (closed) "

Acceptance criteria

• Implemented code changes don't diverge from the related issue.
• Version number is incremented according to SemVer. (Snapshot versions are not merged/released.)
• Pipeline still works.
• GitLab issue is up-to-date.

Proposed squash commit message

Add ecmr-datamodel dependency to ecmr-backend

Add ecmr-datamodel dependency to pom.xml Add olf package registry under repositories section to pom.xml