* add public func to lookup a ChatClient by its clientId
* add facility to send a system message directly to a user
* add clientId field to UserEvent
* implement simple http endpoint to send a message to a user
* let mux handle new directSystemMessageToUser endpoint
* add ClientId to UserEvents across the codebase
* render body of system-message to client
* add clientId to Chat-Message
* add tests showing how url-parsing should work
* add simple rest endpoint helpers for parameter-parsing and easy routing
* use newly added rest-endpoint helper to rout to Client-Messaging controller
* use safe "ReadRestUrlParameter" to parse ClientId
* remove empty HandleFunc in router
* set Header directly to prevent built-in (platform-dependent) canonicalization to kick in
* fix typo in "Parameter" message
* remove debug-logging of HTTP headers in REST-helpers
* convert to uint32 to prevent overruns when converting to wraptype uint later on
* resolve linter-ouchies
* resolve linter potential nil-deref warning
* document the SendSystemMessageToClient endpoint in swaggerdoc
* remove clientId assignment causing potential nil dereference in userDisabledEvent-case
as the clientId isn't relevant here anyway
* make findClientById private, so its not accessible outside of core/chat
* remove redundant string type hint
* Update PR based on linter requirements
Co-authored-by: Raffael Rehberger <raffael@rtrace.io>
Co-authored-by: Gabe Kangas <gabek@real-ity.com>
