Expose crate-specific error type for AMQP, AMQP-based crates

[heaths]

Based on discussions about whether to add any ErrorKind (consensus was "no"), we should (at least consider) exposing crate-specific errors from azure_core_amqp instead of ErrorKind::Amqp, which then forces doing the same for azure_messaging_eventhubs and azure_messaging_servicebus. Based on guidelines this is allowed; though, I need to update those a bit - the gist is there.

The requirement is that you MUST implement From<azure_core::Error> because you will consume methods that return it, most likely. You SHOULD implement From<YourError> for azure_core::Error as well, even if it means just wrapping the error with ErrorKind::Other.