feature: Handle error 429 when connecting websocket

[Jonnern]

A RateLimitGuard can be used to limit (re)connection of sockets.
This works well until the server returns 429 and the client continues to use the configured client rate limit.
If the client is too eager to reconnect, the client may be stuck in a 429 rate limit loop.

This feature enables setting SocketExchangeOptions.ConnectDelayAfterRateLimited which will set a RetryAfterGuardon the connection when the server returns 429.

• Parse error message thrown from ClientWebSocket.Connect when connecting the socket fails
  • Check if "429" is in the error message
• Add RateLimitItemType to RetryAfterGuard
• Add SocketExchangeOptions.ConnectDelayAfterRateLimited
  • Works as a one-time rate limit to avoid subsequent connection attempts that pass the regular connection rate limiting

Note: I could not create a unit test for this behavior.

[JKorf]

Would it be good to use a compiler directive here checking for .NET 6 or higher which uses the new HttpStatusCode property and if lower version fallback to checking for 429?

[Jonnern]

I like that idea