* first draft attempt at adding role assumption option
* refinements
* const not var
* clean up asserts
* set explicit sts endpoint and clarify required inputs error message
* streamline mocks
* add new inputs to Action definition
* ignore .idea directory
* add initial assume role test
* make tests fail usefully when not in GitHub Actions
* add logic to handle suppression of stack trace
* pull credentials exports out into function
* convert environment variable patching to use object for source and add needed members
* add test for STS call
* compartmentalization and use custom user agent in role assumption STS client
* change DO_NOT_SUPRESS_STACK_TRACE to SHOW_STACK_TRACE
* update role-to-assume input description
