backupdr: fix restore resource_manager_tags drop

[Megha-Bose]

backupdr: fixed issue where `google_backup_dr_restore_workload` dropped `resource_manager_tags` during restore requests, causing tags shown in plan to not be applied to restored resources

[github-actions]

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[Megha-Bose]

Adding manual test run logs here as the restore tests could not be added in the CI pipeline. See #16080 for context:

terraform-restore-regional-disk.log
terraform-restore-vm-props.log

[github-actions]

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[roaks3]

Code seems good. Is there a reason we need to support each of Map, Set, and List? Why are labels implementing all of these? It might make sense to rename processLabels if it is no longer being used just for label fields?