Convert observed data to xarray.

def observed_data_to_xarray(self):
        """Convert observed data to xarray."""
        if self.observed is None:
            return None

        observed_data = {}
        if isinstance(self.observed, self.tf.Tensor):
            with self.tf.Session() as sess:
                vals = sess.run(self.observed, feed_dict=self.feed_dict)
        else:
            vals = self.observed

        if self.dims is None:
            dims = {}
        else:
            dims = self.dims

        name = "obs"
        val_dims = dims.get(name)
        vals = np.atleast_1d(vals)
        val_dims, coords = generate_dims_coords(vals.shape, name, dims=val_dims, coords=self.coords)
        # coords = {key: xr.IndexVariable((key,), data=coords[key]) for key in val_dims}

        observed_data[name] = xr.DataArray(vals, dims=val_dims, coords=coords)
        return xr.Dataset(data_vars=observed_data, attrs=make_attrs(library=self.tfp))