Refactor course authoring test pipeline configuration

[bszabo]

This is an incremental merge along the path to enabling Datadog synthetic tests to automatically run immediately after deployments of the course authoring MFE.

It builds on two recent, related PRs:

https://github.com/edx/edx-internal/pull/12296
#21

The functionality added by this PR pertains to configuration. Specifically, configuration as to which tests ought to be run belongs in a GoCD config repository YAML file, and not in the tubular script responsible for triggering the tests and collecting test results. This follows from the observation that we want to preserve the option to customize what tests are run, and what the timeout for those runs is, on a GoCD pipeline by pipeline basis. Each pipeline will have its own YAML file, but the tubular script will be shared across pipelines.

Testing:

Equivalent code was tested on the test-GoCD servers using edx/tubular and edx-gocd-synthetic-testing repos, under bszabo/testing-args-from-gocd branches.

This code will be tested on the stage environment post-merge without possible harm to prod.

Testing entails:

1. Verifying that a new release_tests_1_pipeline pipeline has been added to the st_1_group pipeline group
2. Verifying that four tests run and pass when the stage environment pipeline group is run
3. Verifying that disabling the pipeline feature switch causes the test pipeline to return much faster, without waiting for all four tests to complete, and also that a line is logged flagging the behavior