ADD a COADD2D parset for `weight_method` parameter when using the `optimal_weights()` method

[debora-pe]

As title. See code here:

PypeIt/pypeit/coadd2d.py

Lines 1499 to 1500 in 8d13753

	# TODO add a parset for weight_method in optimal_weights. The default is currently 'auto'
	_, self.use_weights = self.optimal_weights(self.obj_id_bri)