execute_batch adding save_result even if already present

[clausmichele]

Currently execute_batch doesn't check if there is already a save_result node and add one with geoTIFF automatically if nothing provided as parameter to it. It should be aligned with download, which has been fixed some time ago.

Related issue: #240

Here is the line of execute_batch where it adds a save_result:

openeo-python-client/openeo/rest/datacube.py

Line 1878 in 07b869c

out_format = guess_format(outputfile) if outputfile else "GTiff"

The check of download to replicate:

openeo-python-client/openeo/rest/datacube.py

Line 1827 in 07b869c

if self.result_node().process_id == "save_result":

[clausmichele]

I didn't notice there was already another issue for this here #401