Port middleware connectors to the orchestrator (#2970)

This PR ports all the connectors from the `aws-smithy-client` crate into
`aws-smithy-runtime` implementing the new `HttpConnector` trait. The old
connectors are left in place for now, and follow up PRs will remove them
as well as revise the generated configs to take `HttpConnector` impls
rather than `DynConnector`.

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Co-authored-by: Zelda Hessler <zhessler@amazon.com>