Initial WebSockets implementation.

[LarryOsterman]

Create a WebSockets transport implementation for Azure Core.

The Cognitive Services team requires support for WebSockets to complete their move to Azure Core.

This pull request has two sets of changes

1. A complete implementation of the WebSockets protocol
2. A set of changes required to pass the CI gates with the WebSockets protocol changes.

The WebSocket protocol is implemented in the Azure::Core::Http::WebSockets::_internal::WebSocket class. It depends on a WebSocketTransport class and the existing HttpTransport class and uses our existing Http Pipeline technology for the initial WebSocket protocol exchange.

Note that this PR is going into feature/websockets and NOT into main. As a consequence, it is extremely hard for parts of this PR to be extracted and submitted separately.

[gearama]

a few comments

[RickWinter]

Done :)