[VBS] Volume Backup Service - EoL -warning for related tf-providers

[uli-schneider]

Description of the enhancement

Regarding to OTC release notes:
Volume Backup Service –
End-of-Life on 01.08.25

The successor CBR (CloudBackup&Recovery) is already available, since years.

It would be helpful to have a "depricated" - "Warning" during terraform plan,
(similar e.g. VPC-Shared SNAT - Message)

Releated providers might be:
https://registry.terraform.io/providers/opentelekomcloud/opentelekomcloud/latest/docs/resources/vbs_backup_v2
https://registry.terraform.io/providers/opentelekomcloud/opentelekomcloud/latest/docs/resources/vbs_backup_share_v2
https://registry.terraform.io/providers/opentelekomcloud/opentelekomcloud/latest/docs/resources/vbs_backup_policy_v2

Please add also an hint in related tf-documentation pages, about EoL for this service.

If you have any question, please contact the related Productmanager or me.