[uss_qualifier/reports] Ability to specify requirements to validate to test step fragments

[mickmis]

See this discussion for some additional context.

Sometimes we have test step fragments that we use in scenario that validate some requirements.
However, depending on the context in which the fragments are invoked, we sometimes need to validate other additional requirements.
Currently to do so, we resorted to use a pattern of main and sub checks.
Being able to replace this pattern with use of test step fragment requirement would clarify and simplify some parts of the implementation.