Add an option of automatic pings and pongs to web sockets in HtttpClient backends

[adamw]

Consider the same in other backends, as well

Source: https://softwaremill.community/t/websocket-state-monitoring/308

[adamw]

The sttp.ws.WebSocket already sends Pong frames when a Ping is received, when using e.g. the receiveDataFrame method.

Typically it's the servers that send Pings, not clients, and we don't have a way of scheduling these sends as this would require starting a background thread/fiber - which is not something we can always do.

So in typical scenarios things should work as expected; non-typical scenarios will require Pings to be sent manually.