* Introduce a `ClientRSocketConnector` to represent a common logic for
client side connection and management an obtained `RSocket`
* Rework the `RSocketOutboundGateway` to perform similar RSocket request
logic on the server side as well.
* Refactor `RSocketOutboundGatewayIntegrationTests` to demonstrate that
RSocket requests work the same way from the server side as well.
For this reason a `CommonConfig` has been extracted with the same
`RSocketOutboundGateway` configuration reuse on both server and client
sides.
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