Allow for Herbst-Schorfheide and DS-MH sampler

See https://forum.dynare.org/t/new-samplers-and-mode-compute-methods/17267/7

First part is done in !1884 (merged)

• The default options for the samplers need to be added to default_option_values (done in 128eaa2d)
• The two routines currently do not provide any return arguments/output