http3 client.
Note the client does not do dns resolve but blindly sends requests
using connections created by the connector.
Used for sending HTTP request directly.
h3 client connection, wrapping inner types for ease of use.
All request will be sent to the connection established using the connector.
Currently connector can only connect to a fixed server (to support grpc use case).
Expand connector to do resolve different server based on uri can be added in future.
Use the host:port portion of the uri and resolve to an sockaddr.
If uri host portion is an ip string, then directly use the ip addr without
dns lookup.