Add stubs to make SRA test fully runnable (#2519)

* add: stubs to make sra test fully runnable (but not useful 😅

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* fix: disable build.gradle enableNewSmithyRuntime option

* fix: clippy lints
add: feature gate for test connection

* fix: doc comment

* move: connections module from API to runtime

* update: TODO message
add: exceptions for external types

* Fix external types lint

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