Add functionality to generate confusion matrix on backend

[natestemen]

In REM, we have a handy function to generate a confusion matrix when the probabilities of bitflips are known:

mitiq/mitiq/rem/inverse_confusion_matrix.py

Lines 74 to 78 in 7984127

	def generate_inverse_confusion_matrix(
	num_qubits: int,
	p0: float = 0.01,
	p1: float = 0.01,
	) -> npt.NDArray[np.float64]:

Adding a function that generates the inversion confusion matrix when the parameters $p_0$ and $p_1$ are not known would aid users in using REM when using real backends with limited knowledge.

Requirements

1. Decide best way to "learn" $p_0$ and $p_1$ parameters, especially when they may differ across qubits.
2. Add a function to mitiq/rem/inverse_confusion_matrix.py that allows a user to generate an inverse confusion matrix on a specified backend (using an executor). This function should optionally return $p_0$ and $p_1$.

---

This idea came out of discussion with @ecarlander and @ruheenirodi.