Make it possibility to add Gradle settings file (init.gradle) for Gradle configuartion with credentials.
Integrate with the config file provider plugin
Easy to add, but you can do this today with the type "custom file".
But I guess what you really want is also the integration into the jenkins gradle plugin  - if so, then you should open a feature request for the gradle plugin to integrate with the config file provider plugin. For this case, the config file provider plugin already provides an extension point  that should be integrated by the gradle plugin.
New feature request for the gradle plugin: