Release pipeline

[sjorsholtrop-ritense]

Adds release.yml workflow to release new versions of Valtimo backend and frontend in lock-step.

Workflow must be run manually from a release/* branch.

The workflow will build, test and release the frontend and backend libraries. Then it will build the frontend/backend images based on the GZAC implementation template in this repo, and push them to GHCR and Dockerhub (ritense/gzac-backend, ritense/gzac-frontend).

Secrets for Dockerhub login have been added to the repo.

[ThomasMinkeRitense]

@sjorsholtrop-ritense two remarks:

• I'd like the version to be derived from the branch name. If I release from branch release/13.6.0, version should just be 13.6.0
• We can't use the publish to Docker Hub yet without cleaning up the configuration files and the test classes that are in the app module. I'd like to discuss this step with the team as well because I heard some concerns about publishing the development app to be our production worthy product.

[sjorsholtrop-ritense]

Still blocked on cleaning up the frontend app by making it not include dev/test-only routes and components when building for production.

[sjorsholtrop-ritense]

Seems to work now. Tested it here: https://github.com/valtimo-platform/valtimo/actions/runs/20620909414

Publishing the frontend went wrong because I cannot publish over an existing 0.0.0 release, which was released in an earlier attempt.
Publishing the backend didn't work because I dropped the deployment.
But publishing the image worked fine for both: ritense/gzac-backend:0.0.0 and ritense/gzac-frontend:0.0.0. We can test those images now.

The last step in the pipeline, creating the GitHub Release, hasn't run yet. But I'm sure it'll work as it's just:

- name: Create release
  uses: softprops/action-gh-release@v1
  with:
    tag_name: ${{ needs.prepare.outputs.version }}
    name: ${{ needs.prepare.outputs.version }}
    body: "Release for Valtimo version ${{ needs.prepare.outputs.version }}."
    draft: false
    prerelease: false