Update documentation for gradle plugin classes

[sreich]

Hi, I understand that the docs for the fields are available here: https://github.com/OpenLiberty/ci.gradle/blob/main/docs/libertyExtensions.md

However, when looking at the code and sources on my end, the gradle extension files do not have any documentation on any of them https://github.com/OpenLiberty/ci.gradle/blob/main/src/main/groovy/io/openliberty/tools/gradle/extensions/ServerExtension.groovy

It's my expectation that I'd be able to just ctrl-click from my editor to dive into the sources/docs for this, or on mouse over, to view the docs and purpose for each field

I'm not sure about the documentation behaviors for gradle groovy plugins, personally I prefer kts kotlin ones, so maybe the kotlin docs behave better in that way. In my experience, at least for the latter, the plugin classes generate their docs nicely and mouse over for docs or ctrl-click for symbol nav, all behave like other Java classes do. Dunno if groovy is limited here or not?

But either way, at least having some comments on some of the fields would be a big improvement from what's here now