Follow DMTF redfish deprecation on StorageControllers (#7081)
* Get controller information from "Controllers" field instead of "StorageControllers" which is deprecated
* Add changelog fragment
* Changelog fragment writing guide formatting
* For consistency, get_disk_inventory and get_volume_inventory use Controllers key instead of StorageControllers to obtain controller name
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Co-authored-by: Pierre-yves FONTANIERE <pyf@cc.in2p3.fr>
(cherry picked from commit fe3eec0122)
Co-authored-by: Pierre-yves Fontaniere <pyfontan@cc.in2p3.fr>
