[Feat]: enable partially execution of the action

[AndreasAugustin]

Describe the feature

Would be nice to have the possibility to only execute some partial steps within the action.

e.g.

 - name: Test action step
        uses: AndreasAugustin/actions-template-sync@v1
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          source_repo_path: AndreasAugustin/template.git
          steps: pull,commit  # define the steps to execute

With this people are able to use different actions with the current workflow steps

Use Case

Sometimes people want to be able to have some actions, commands executed in between the step (e.g. discussion #467, or https://github.com/cookiecutter/cookiecutter).
With the possibility of the split something like

- name: Test action step
      uses: AndreasAugustin/actions-template-sync@v1
      with:
        github_token: ${{ secrets.GITHUB_TOKEN }}
        source_repo_path: AndreasAugustin/template.git
        steps: pull  # define the steps to execute
- name: step in between
  run: sed -i "s/foo/\/bar/g" "*.md" \;
- name: Test action step
    uses: AndreasAugustin/actions-template-sync@v1
    with:
      github_token: ${{ secrets.GITHUB_TOKEN }}
      source_repo_path: AndreasAugustin/template.git
      steps: commit,push,pr  # define the steps to execute

would be possible.

The difference to the hooks would be that the people would also be able to use other github actions in between.
(currently possible with hooks e.g. use exit 0 in hook, but not super convenient. 🥷 )

Proposed Solution

No response

Acknowledgements

• I may be able to implement this feature request

[kdeldycke]

Oh. Now I get what you meant in #467. That would be indeed a super-powerful feature. I'm ready to test it as an alternative to hooks if you have a prototype.

[AndreasAugustin]

Remark:
Some preparations are also done within #498 because we need to have proper permissions on the runner after using the action (e.g. #484 ) or else the feature is kinda useless

Update
prerequisites should be done with #498 and the refactoring part.