This adds in a variable passing mechanism to change the TEST_COLLECTION_CONFIG for each provider. Now that all providers are using the same generated file, it isn't a straight constant.
Due to GitLab seeming to explode the values of File-Type variables when passed between jobs, we use a "clever" approach of passing the variable name and indirectly accessing the temporary filename for the TEST_COLLECTION_CONFIG. To prevent any accidents, there's also a check that the TEST_COLLECTION_CONFIG is actually a file, and not the contents themselves.