Allow setting GitHub commit status using ssh key.

[a-t-0]

Currently, a GitHub personal access code is used to set the build status of the GitHub commits on which the GitLab CI is ran. This is done in function:

get_github_personal_access_token

and the ability to set the build status of the GitHub commits is verified in:

custom_set_build_status_of_github_commit

• Determine what the minimal permissions need to be to set the build status of a commit.
• Automatically create an ssh-key that is able to set the commit build status of arbitrary repos within the GitHub username/organisation. (Re-use the code in src/helper_ssh.sh for this purpose).