Add connection poisoning to aws-smithy-client (#2445)

* Add Connection Poisoning to aws-smithy-client

* Fix doc links

* Remove required tokio dependency from aws-smithy-client

* Remove external type exposed

* Rename, re-add tokio dependency

* Change IP to 127.0.0.1 to attempt to fix windows

* Add dns::Name to external types

* Remove non_exhaustive not needed

* Add client target to changelog