Follow-up to the proposal from rsandell
The easiest way would be to....
- Add a new "hpi.pluginDocumentationUrl" property to Maven HPI Plugin (similar to hpi.pluginChangelogUrl and hpi.pluginLogoUrl in 3.8)
- Update Jenkins Update Center to take this property into account while generating plugin-documentation-urls JSON
- Update GitHubExtractor in Plugin Site API to properly process custom URLs. A new extractor might be required