Add GH App Auth support

[MatteoManzoni]

This PR introduces the support for GH App Auth in the action.
With the support to GH App Auth this action should be able to require less privileges than org:admin which, in many cases, is deemed too broad to be used.

The input requirements of the modified action to use GH App Auth are:

• gh_app_secret_key: the RSA secret key generated during the App creation process used to sign App JWT tokens
• gh_app_ID: GH App ID
• gh_app_installation_ID: Installation ID of the App on your org

[leonsteinhaeuser]

@MatteoManzoni thank you very much for providing this solution. I would like to ask you to write a few sentences in the README.md so that others can understand what they need to do to use this feature.

[MatteoManzoni]

Sure @leonsteinhaeuser, I've totally forgot. I'll add documentation for the new variables and a new paragraph with GH App specific instructions, soon.

[MatteoManzoni]

Hey @leonsteinhaeuser, I've update the README, let me know if you have any feedback

[leonsteinhaeuser]

@MatteoManzoni first of all great work.

When I added this function to the release-v1.2.0 branch and created a pre-release version from it, I found in my testing that the action.yml file pointed to the wrong script.

 /home/runner/work/_temp/f4f8965b-ec35-40a2-ae04-ecd5ab7ed8e3.sh: line 27: /home/runner/work/_actions/leonsteinhaeuser/project-beta-automations/v1.2.0-alpha.1/ghapp_credential_helper.sh: No such file or directory
could not prompt: EOF
25l? How would you like to authenticate GitHub CLI?  [Use arrows to move, type to filter]
> Login with a web browser
  Paste an authentication token
25h

Since it was just a typo, I fixed it so we can release this feature soon.

[MatteoManzoni]

@MatteoManzoni first of all great work.

When I added this function to the release-v1.2.0 branch and created a pre-release version from it, I found in my testing that the action.yml file pointed to the wrong script.

 /home/runner/work/_temp/f4f8965b-ec35-40a2-ae04-ecd5ab7ed8e3.sh: line 27: /home/runner/work/_actions/leonsteinhaeuser/project-beta-automations/v1.2.0-alpha.1/ghapp_credential_helper.sh: No such file or directory
could not prompt: EOF
25l? How would you like to authenticate GitHub CLI?  [Use arrows to move, type to filter]
> Login with a web browser
  Paste an authentication token
25h

Since it was just a typo, I fixed it so we can release this feature soon.

@leonsteinhaeuser thank you so much, that was definitely a typo

[leonsteinhaeuser]

@MatteoManzoni this feature is now available with version v1.2.0

[MatteoManzoni]

Thank you so much @leonsteinhaeuser