Add Support for TestPlan

[SaketGupte]

Is your feature request related to a problem? Please describe.
iOS introduced feature called TestPlan back in 2020. It allows for running Unit and UI Test multiple times with different configurations.
Configurations can be different language and region or Simulated location. Think of LTR and RTL snapshot tests.
Without TestPlan each configuration would require scheme. With TestPlan you can have all the configurations run together.

Describe the solution you'd like
Marathon should support TestPlan as well.

Additional context
A more detailed explaination of what a TestPlan is can be found here: https://useyourloaf.com/blog/xcode-test-plans/

[Malinskiy]

Marathon has it's own test filtering and scheduling system. I don't really understand why there is a need to use custom formats that are not even well documented: xctestrun file is only documented in manpages and even then the docs do not match the implementation.

If the source of truth for test list is xctestrun for users then an additional utility is needed that transforms testplan into a simple line-by-line list of tests that can be recognized by marathon https://docs.marathonlabs.io/configuration/filtering#values-file-filtering