Add jspecify Nonnull/Nullable annotations

[moonfruit]

The spring-framework has now abandoned its own definition of Nonnull/Nullable annotations in favor of those defined by jspecify.
As one of the most successful Java open source project, I'm sure more and more people will follow it and start using jspecify.
So I think it's important for lombok to provide predefined configuration templates for jspecify to simplify its use.

[Rawi01]

Thanks for your contribution 👍

• Please update the comment in ConfigurationKeys and the documentation in configuration.html to include the new key
• Please add yourself to the AUTHORS file

[moonfruit]

OK. I'm done. Please help me check if there are any more changes that need to be made.

[knutwannheden]

At some point it would be awesome if Lombok could support scoped annotations like JSpecify's @NullMarked. Without that I doubt that Lombok will be able to leverage JSpecify very much.

[rzwitserloot]

This has been merged as commit 0d0aba6. Not quite sure why github hasn't picked up on that.