process
Register a handler which will be triggered with a list of all markdown pages in this project.
IMPORTANT: This will only be markdown that represents a page. If you generate markdown that becomes a non-page composable, it won't be triggered by this callback.
The markdown files will be partially parsed to include front matter information, plus additional metadata that could be useful for generating some additional content, such as a top-level listing page that links to all markdown pages.
If set, this will run before all markdown files are converted (meaning you can potentially add an additional markdown file as a result of this call, although normally we expect users will just generate Kotlin files).