Given a minimal supercuspidal representation π of GL2(Qp), this returns a cuspidal inducing datum
that gives rise to π.
Recall (from Section Supercuspidal Representations) that a cuspidal inducing datum (K, Ξ) consists of a
subgroup K of GL2(Qp) and a representation Ξ of K that gives rise to π via induction.
Importantly, Ξ factors through some finite quotient K/K1 of K.
This function returns such a representation of K/K1.
From this one can deduce the representation on K, and hence π.