Add support for: XCUITest .xctestplan

[TomVanDerSpek]

🚀 Feature Proposal

Xcode introduced Test Plans in 2019 during its WWDC event. Would help a lot if this is also supported by SuaceLabs.

Motivation

We currently have to maintain two lists on which tests to run, one in our XCTestPlan and one in the .sauce/config. This comes with a risk that these lists will get out of sync. Also renaming a test class or its tests are automatically updated inside of the XCTestPlan. This is not automatically done in the .sauce/config and therefor a risk of unneeded pipeline failures.

Example

suites:
  - name: "Integration Tests"
    testOptions:
      xctestplan: AppIntegration

[ianrhamilton]

@TomVanDerSpek if you're using Fastlane I created fastlane-plugin-saucectl for my current project that uses saucectl which allows you to use xcode testPlans. The config.yaml can be automatically generated by the plugin for ci builds. Check out the docs here. It's fairly new, but going well on a couple of projects now. Any issues, let me know!