Fix missing metadata for nested POJO

[snicoll]

Because Compression is in a separate module, the annotation processor can't read its source model and we don't have metadata for those keys.

I've had a lame attempt at documenting one property but @izeye caught that :)

We should either configure the build to fix this or we should move the documentation to manual metadata. Right now, Compression is documented as if it was picked up by the AP and that's rather confusing.

I think a handful of other POJOs are affected (Ssl comes to mind).

[snicoll]

We've decided to fix the metadata manually for the time being. We can't fix this properly without introducing a breaking change so it's too late for 2.1. I've opened #14679

[snicoll]

Turns out this is applicable to the following namespace: management.server.ssl, server.compression, server.http2, server.servlet.jsp, server.servlet.session and server.ssl.