Document the ability to disable KeepAlive

[fyrkov]

It is not clear if it is possible to disable KeepAlive behavior for a connection and if yes how to do that. I would expect that it is possible by providing a client config like:

RSocketConnector.create()
                .keepAlive(0, 0)

and the corresponding code in the io.rsocket.core.RSocketRequester

The documentation says however that the KeepAlive must be send by a client: https://rsocket.io/about/protocol/#keepalive-frame-0x03

Documentation Issue

The current state of javadocs does not reflect if there is such ability: io.rsocket.core.RSocketConnector#keepAlive

Improvement Suggestion

Update javadocs with inforamtion how to disable KeepAlive (if possible)

Additional context

As far as I understand the keep alive behavior is not needed when there is no more than one request/response expected.