This commit adds a new auto-configuration for RSocket support in Spring
Integration.

Given an application with `spring-messaging`, `spring-integration-rsocket`
and RSocket dependencies, developers are now able to leverage Spring
Integration features with RSocket.

It is now possible to configure an RSocket server with
`"spring.rsocket.server.*"` properties and let it use
`IntegrationRSocketEndpoint` or `RSocketOutboundGateway` components to
handle incoming RSocket messages. This infrastructure can handle Spring
Integration RSocket channel adapters and `@MessageMapping` handlers
(given `"spring.integration.rsocket.server.message-mapping-enabled"`is
configured.

If the `"spring.integration.rsocket.client.host"` and
`"spring.integration.rsocket.client.port"` (for TCP protocol), or
`"spring.integration.rsocket.client.uri"`  (for WebSocket) is configured
then a `ClientRSocketConnector` will be configured accordingly.

Closes gh-18834
Co-authored-by: Brian Clozel <bclozel@pivotal.io>