add connection poisoning support to the orchestrator (#2824)

This PR updates the orchestrator to support connection poisoning for the
`hyper` connector. It also renames many usages of "connection" to
"connector" in order to make talking about these concepts less
confusing. In short:

```
/// A "connector" manages one or more "connections", handles connection timeouts, re-establishes
/// connections, etc.
///
/// "Connections" refers to the actual transport layer implementation of the connector.
/// By default, the orchestrator uses a connector provided by `hyper`.
```

One possibly controversial decision I made is that `reconnect_mode` is
now a standalone configurable field, rather that a sub-field of
`RetryConfig`. I think we should get together as a team and discuss what
kinds of things we want to allow users to do when configuring
connections.

My thoughts on this are that we should either:

- **A.** Make connection-related settings their own types instead of
including them within other config types
- **B.** Make a single config struct for all connector-related stuff/use
the preëxisting `ConnectorSettings` struct.

Personally, I'm partial to A.

----

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Co-authored-by: John DiSanti <jdisanti@amazon.com>