Added information how to use JsonFilter
Added information how to use JsonFilter

Creating a query hint to use JsonFilter that will choose
required backed to create a volume was complicated.
Added description how to use that will be helpful for others.

Change-Id: If04f037cf55b5b9d116927aa4b23a9c42d7b53e6
Co-authored-by: Bartosz Rabiega <752785f3331c6024a2621d18de0c79e7c5a858e6@corp.ovh.com>

mahak/cinder,openstack/cinder,mahak/cinder,openstack/cinder