UTP11 — Rework of TestArchitecture section

A master issue for the rework of test architecture package. Several issues will be merged into this issue to improve readability and understandability of the resolutions

Incorporate the issues 15644, 15648 and 15910. The first two issues targets the fact the Scheduler is never part of the test model by definition. Therefore, it represents a pure tooling concept which has nothing in common with a domain-specific profile. The resolution for this is to remove the Scheduler from the profile section and to put it into the annex.
The last issue deals with a semantically necessary precision of a TestContext. Currently, a TestContext is only required to be an instance of uml::StructuredClassifier. Since a TestContext must have the ability to contain operations and classifier behavior, the UTP has to ensure that each instance of a TestContext is both a StructuredClassifier and BehavioredClassifier (e.g. Class, Component…).