Different repositories and different targets may depend on certain env. variables to run test in different ways. Instead of specific logics for each env. variable, we should have a generic support for different env. variables.

Ideal case, people just define these values in .ci.yaml targets, and these values will be auto populated to ENV when running tests.

Example env. variable support:

• channel in packages, logic in recipes
• package_sharding in packages, logic in recipes