feat: Add support to read test options from a config file

[mayankshah1607]

What would you like to add?

Once linkerd/linkerd2#4532 gets merged, it would be great to have the tests read a config, ideally a yaml file that defines configuration options for things like ingress controllers, allow tests, disable tests, verbose, etc.

How should this be done?

In case of Sonobuoy, we may want the users to create a configMap object in the sonobuoy namespace to hold this yaml config file. We then mount it using the podSpec property on the Sonobuoy plugin file. With the help of K8s client-go, the tests may then read the config first and run tests accordingly.

If users wish to plug in the config file outside of Sonobuoy, i.e, running the tests locally, an optional flag --config-path may be used. The tests then pick-up the config file from the value of the flag if no configMap is found. In the situation where users may want to run the tests locally inside the Docker image provided, an additional volume may be mounted onto the container along with the flag.

[mayankshah1607]

Closed via #1