Augments the auxiliary design with strata dummies (dropping one level) and
appends stratum-share means when user-supplied auxiliary_means are
present. This is the Wu-style strategy of adding stratum indicators to the
auxiliary calibration block in pseudo empirical likelihood for surveys.
el_augment_strata_aux(
aux_design_full,
strata_factor,
weights_full,
N_pop,
auxiliary_means
)