Add Javadoc to configuration options in builder and spec interfaces / classes

[lhotari]

As mentioned in #3, the configuration model in Reactive Java client is different from the ordinary Java client.

It is necessary to have clear Javadoc on all configuration options. There are multiple ways to configure the same option so it should be decided where to document the option and use links to refer to the primary place of documentation.

The proposal is to primarily document the options in the builder interface methods since that is the primary way for using the configuration api in code. The "spec" classes could contain the copy pasted title for the option and a link to the builder interface method for setting the option. The builder could contain more extensive explanations.

[lhotari]

Javadocs have been added by many PRs created by @cbornet . I'm closing this issue.