ci: add backport action

[nicpuppa]

Description of the change

Add backport action to the project https://github.com/korthout/backport-action

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have opened this pull request against the alpha branch
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...]

[nicpuppa]

@jwulf I don't have full access to this project, do we have a PAT token ? If not can you create one ?

[jwulf]

Workflows that run on main get a GitHub token automatically, see here for an example of using it:

https://github.com/camunda/camunda-8-js-sdk/blob/main/.github/workflows/release.yml#L303

[jwulf]

Ah, it looks like if you use that token then no workflows will run on the PR:

https://docs.github.com/en/actions/concepts/security/github_token#when-github_token-triggers-workflow-runs

[jwulf]

Would we not be better off to create a GitHub App for backport token exchange, and use actions/create-github-app-token?

- name: Generate token
  id: generate-token
  uses: actions/create-github-app-token@v1
  with:
    app-id: ${{ vars.APP_ID }}
    private-key: ${{ secrets.APP_PRIVATE_KEY }}

- name: Create backport PR
...
   uses: korthout/backport-action@v4
        with:
          # Token to authenticate requests to GitHub
          github_token: ${{ steps.generate-token.outputs.token }}

We could use this pattern on all the SDKs, and the token is short-lived (one hour).

[jwulf]

Another option would be to use a workflow_dispatch trigger if the backport action creates a PR.

---

Actually, the comment below does not apply to this repository. This repo does not have any generated code in it. But we'll need to figure out a different strategy for the new TypeScript, Python, and C# repos. Maybe changing the way that generated code is committed (maybe excluding it from dev machines and only committing it in a separate commit in CI).

For those repos, at the moment, PRs will include a large amount of generated code. A fix applied to main will be building from the current development specification, with all the generated methods.

[nicpuppa]

the backport action is used in the majority of the repository in camunda, we should use it also here. We just need a PAT token, not sure if you can do it or we need to ask IT

Since now we will have stable branches as well, I think it's a useful tool to have also here and in all the other sdk repository

cc @megglos