fix(aws-sdk): exception handling & test coverage

* Fixes: #136 Unintended exception mishandling after v3 sdk change
* Upgrades test coverage to 100% statement/function/branch/line
* Requires 100% coverage in jest
* Ignore coverage for defaulting of GITHUB_WORKSPACE due to implications
  of test file locations during testing
* Retypes CreateStackCommandInput to affirm presence of StackName
  which is required, and previously asserted by core.getInput()
* Adds dependency on @smithy/node-http-handler which is used in
  src/main.ts but not declared as a dependency, depending on hoisting
  when installed by @aws-sdk/client-cloudformation (consider using pnpm
  instead of npm to avoid this in future?)

Author: Zordrak