As a mongoDB engineer,
I should be able to run the selected_tests_gen task,
and know that it will run all tasks for a given set of related task mappings returned by selected-tests service,
So that I know all tasks that are affected by my code changes will be run

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AC:

• When I run the selected_tests_gen task in my patch build, it runs all tasks related to my file changes (using the task mappings model)
• When I run buildscripts/selected_tests.py locally, it logs which tasks and steps are executed so that other engineers can debug any issues encountered.
• When an execution task(s) and its parent display task are returned by the task mappings endpoint for a given source file, the selected_tests_gen task should know to run only the _gen task associated with that parent display task, not the execution task(s)