Move composites test to DaVinciExamples

The following discussion from !711 (merged) should be addressed:

• @sstahl started a discussion: (+3 comments)

  Thanks for this MR. Do you have plans to include some of the changes in !700 (merged) also here?

https://gitlab.cern.ch/lhcb/DaVinci/-/blob/master/DaVinciTests/tests/options/option_davinci_v2_composites.py is presently the only test building particles. It should be moved to DaVinciExamples once !700 (merged) is merged.