Add QMTest for Det/DetCond/examples/FunctionalConditionAccessor.cpp

The following discussion from !1892 (merged) should be addressed:

• @cattanem started a discussion: (+1 comment)

  @graven, I'd like to tag LHCb today. If you would like this included, please provide an expanded description as requested by @gligorov

  Please don't forget also to add a qmtest to exercise this example. I am happy if you do that later, in which case please resolve this discussion into an issue