Workaround bug in smithy-rules-engine (#2179)

* Workaround bug in smithy-rules-engine

This PR works around a bug in smithy-rules-engine `Parameter.toBuilder()` — the method was discarding the default value (and other fields). This was fixed here: https://github.com/awslabs/smithy/pull/1571/files. Until that's merged, this works around it by copying the value manually. This also adds an SDK adhoc test that includes an endpoint test.

* change to TODO comment