Merge branch 'LHCBGAUSS-838.AmpGen' into 'Sim09-Upgrade'

LHCBGAUSS-838: New Amplitude model for D -> pi pi pi

New Amplitude model from @tevans. Changes in requirements and cmake build added (made with @clemenci).

Details at LHCBGAUSS-838

See merge request !26 (merged)