[OBS] - Inventory - Support OptionalField and SMN Support

[uli-schneider]

Description of the enhancement

In Console OBS function for inventory offers the possible:

(1) Configure Optional Fields the the inventory report
(2) Set a notification if a new inventory is available

API Description for the Fields:
https://docs.otc.t-systems.com/object-storage-service/api-ref/apis/advanced_bucket_settings/configuring_bucket_inventories.html

Please add them to:
https://registry.terraform.io/providers/opentelekomcloud/opentelekomcloud/latest/docs/resources/obs_bucket_inventory

Thanks in Advance