Add test to ensure all configurations defined on artifacts.Config are reloades

[AndersonQ]

Describe the enhancement:

#3937 adds a test ensuring the current artifact.Config is all reloaded. However it cannot account for future additions on the struct or settings. Therefore a test which verifies all properties on artifact.Config are tested must be created.
So far the idea is the test should ensure the current test uses all possible configurations/keys rather than generating a random config file from artifact.Config.

Describe a specific use case for the enhancement or feature:
If artifact.Config is updated, the new fields won't be covered by tests.

What is the definition of done?

A new property added to artifact.Config will cause the test of the upgrade reloader to fail.

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)