This commit calls the `useSystemProperties` method on the HttpAsyncClientBuilder so that the jvm
system properties are used. The primary reason for doing this is to ensure the builder uses the
system default SSLContext rather than the default instance created by the http client library.
Closes#23231
Using the infra that we now have in place, we can convert the low-level REST client docs so that they extract code snippets from real Java classes. This way we make sure that all the snippets properly compile. Compared to the high level REST client docs, in this case we don't run the tests themselves, as that would require depending on test-framework which requires java 8 while the low-level REST client is compatible with java 7. I think that compiling snippets is enough for now.
This commit converts the low level client and high level client chapters into two parts, which allows each high level client supported api to be on a separate page and show up in the index on the right.
The REST Client is split into 2 parts:
* Low level
* High level
The High level client has a main common section and the document delete API documentation as a start.
Tanguy Leroux
Jay Modi
Luca Cavanna
David Pilato