I'm trying to automate the api endpoints added under "Configure System". I believe the plugin is https://wiki.jenkins.io/display/JENKINS/GitHub+Branch+Source+Plugin. (v.2.4.2). The property is simply left out.
I'm also experiencing this https://issues.jenkins-ci.org/browse/JENKINS-54051 when trying to add the api, although when using the setting it works as expected.
Jenkins is set up with https://github.com/helm/charts/tree/master/stable/jenkins, haven't really tweaked anything particular, but these are the plugins I provide:
Also, running Jenkins ver. 2.164.