testing: Add support for runtime environment variables to GitHub Workflows

GitHub Workflows is the preferred test driver for tests in this repository, but the current workflow implementation has several limitations. One of them is the ability to set runtime environment variables that are specific to a Workflow.

## Approach

Options:
1. Hard code a central map of environment variables, and refactor code to ensure clean namespacing
2. Create a mechanism to pass environment variables to our reusable test workflow

Option 2 is the most versatile with the least need to refactor existing code.

Option 1 has the further downside of placing test-specific parameters in a central file. I'm not sure if any changes to `test.yml` are triggering wide-scale test execution currently, but with this approach we'd likely need to trigger more tests from any change, which would include adding environment variables for unrelated tests.

@pattishin has asked that as part of the PR fixing this issue, we look for existing hard-coded values and shift them to environment variable configuration.

This issue is a blocker on implementation of GHA-based test workflows for a number of samples, with #3149 as the driver for research today.