Extend two qubit gate error model to cover all Pauli errors

[Naphann]

Currently, two qubit gate error model in QuISP only have 9 possible types of errors.

quisp/quisp/modules/QNIC/StationaryQubit/StationaryQubit.ned

Lines 57 to 66 in bd4c706

	double cnot_gate_error_rate = default(0);
	double cnot_gate_iz_error_ratio = default(1);
	double cnot_gate_zi_error_ratio = default(1);
	double cnot_gate_zz_error_ratio = default(1);
	double cnot_gate_ix_error_ratio = default(1);
	double cnot_gate_xi_error_ratio = default(1);
	double cnot_gate_xx_error_ratio = default(1);
	double cnot_gate_iy_error_ratio = default(1);
	double cnot_gate_yi_error_ratio = default(1);
	double cnot_gate_yy_error_ratio = default(1);

We probably would want the full 15 possible combinations of {I, X, Y, Z} * {I, X, Y, Z} - II errors, each with assignable weights.