Use test plans for tests

[mathebox]

Is your feature request related to a problem? Please describe.
With Xcode 11, testplans were made available to better configure the tests to be executed.

Describe the solution you'd like
Adopt testplans with a reasonable configuration to the extra target for UI tests / making screenshots can be removed.

Additional context

• https://useyourloaf.com/blog/xcode-test-plans/
• This might influence Run all UI tests via Github Actions #827
• This might break the automatic screenshot creation via fastlane.