Ability to pass permissions as comma separated list

[chkp-sergeyl]

The permission-{permission_name} has to be passed one by one to the action.
This makes it impossible to wrap this action with some other logic into a composite action, that can be distributed. For example, when the credentials of a github app are not taken from a github secret but from a different secret store.

If we pass permissions as a comma separated list we can have something like the following:

outputs:
    token: ${{ steps.generate-token.outputs.token }}

... other steps go here...

    - name: Generate a token
      id: generate-token
      uses: actions/create-github-app-token@v2
      with:
        app-id: ${{ steps.get-app-credentials.outputs.APP_ID_KEY }}
        private-key: ${{ steps.get-app-credentials.outputs.PRIVATE_KEY }}
        owner: ${{ inputs.repository_owner }}
        repositories: ${{ inputs.repositories }}
        permissions: ${{ inputs.permissions }}