Document the new "Allow GitHub Actions to create and approve pull requests" setting in the Github documentation

[kastl-ars]

Description

Github nowadays requires an additional repository-level switch in addition to the permissions setting in a workflow to allow Actions or Action tokens to open pull requests.

Repository Settings → Actions → General → Workflow permissions → enable Allow GitHub Actions to create and approve pull requests

Running updatecli in a Github Action creates a branch but cannot create a pull request, if the setting above is not enabled.

The documentation should contain this information in two places:

1. The github scm documentation, which normally contains the authentication details, should contain a note (if the user runs updatecli from a Github Action, this is not required for running locally I guess)
2. The github action documentation should not only mention the token permissions, but also this repository-level setting.

There is a separate issue for the updatecli-action to also add this to the action's README.

Kind Regards,
Johannes