iOS websocket transport example

[whyoleg]

For now, ktor doesn't support websockets on Native, so no support for iOS.
It would be good, to at least create an example transport implementation for that.
For inspiration: example of iOS websockets written in kotlin

From ktor 2.0, WebSockets are supported on native via Darwin and CIO client engines.
rsocket-kotlin version compatible with ktor 2.0 will be released soon, so issue can be closed after it

[whyoleg]

ktor 2.0 supports websockets on CIO and Darwin engines for iOS.
So rsocket-kotlin supports it out of the box starting from 0.15.4