Make fixes to client proxy definitions

[tsmith023]

This PR fixes the definitions of HTTP/1.1 proxies used through httpx and allows for the definition of an HTTP/2 proxy through grpc with a specific configuration. In order to make use of a gRPC proxy, users will have to bare in mind the limitations of Google's official Python grpc implementation.

To summarise, users should reach for Envoy proxy when configuring any gRPC proxy for themselves. (The Weaviate Cloud Service (WCS) in fact uses this solution in some of its deployments.) For this, their docs should be the first place to look as too should our example that works in our CI within ci/proxy/envoy.yaml. In short, the proxy must accept a CONNECT request and mutate it into a POST request that Weaviate can understand.

Example usage:

with weaviate.connect_to_local(
    additional_config=wvc.init.AdditionalConfig(
        proxies=wvc.init.Proxies(
            http="http://localhost:8070",
            grpc="http://localhost:10000",
        )
    )
) as client:
    ...

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