Expose atol and rtol arguments of the operator simplification

[mrossinek]

What should we add?

During the backpropagate method, the observable gets simplified here:

qiskit-addon-obp/qiskit_addon_obp/backpropagation.py

Lines 200 to 202 in 39295a4

	observables_tmp[i], simplify_metadata = simplify_sparse_pauli_op(
	observables_tmp[i]
	)

That function has atol and rtol arguments which are inaccessible via the arguments of backpropagate method. This should be exposed to enable the end-user to customize these tolerances without having to modify the SparsePauliOp.atol and SparsePauliOp.rtol class-attributes.