Introduce a router_service

[o0Ignition0o]

Fixes #1496 eventually.

todo:

• fix tests
• enable APQ
• deal with sandbox and homepage
• decompression
• tracing
• impl TryFrom<supergraph::Request> for Request should put the graphql::Request in the body if the method is POST, and urlencode it in the path if the method is GET
• sure could use a helper to go from a defer chunked payload into a stream of graphql::Response for test purposes (like take the bytes, strip --graphql and everything, and deserialize the json contents), possibly using https://github.com/scottlamb/multipart-stream-rs/blob/master/examples/client.rs#L35
• move back the supergraph_service defer tests
• not happy with from_supergraph_mock_callback_and_configuration and the likes, let's maybe use a builder
• router::Request and router::Response builders
• Update and verify Apollo telemetry

[garypen]

Huge amount of work. Really well done!!

Did you check the diffs of the documentation for public changes? Could you please document the result in the PR so we can see what has been added?

[BrynCooke]

Here's a list of API changes: https://gist.github.com/BrynCooke/590941cc0008dabd40703aca3e9b4e6b

[o0Ignition0o]

@BrynCooke thanks a lot for the diff

Removed items from the public API
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(none)

Changed items in the public API
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(none)

this looks good doesn't it? do we see things that went public and shouldnt ?