INT-1198: WebSockets: Server Side

JIRA: https://jira.spring.io/browse/INT-1198

INT-1198: WebSocket: Add namespace support

Polishing components according to the namespace support experience

Parser for `<server-container>` and tests

INT-1198: Add parser tests for `<int-websocket:outbound-channel-adapter>`

Introduce `use-broker` on server side

Polishing according PR comments

`What's New` note