It is described here:
See https://github.com/arduino/library-registry#adding-a-library-to-library-manager
No, only libraries added to the Library Manager via the process in the FAQ linked above.
I do think it would be smart to automate the process of adding libraries to Library Manager. The current system is pretty inefficient and seems to be quite a bit of work for agdl. It seems like it would be pretty easy to do. Quite frequently there is an issue with the release, metadata, or folder structure of the library so the automated system would need to notify the library author if the process failed.