resource/aws_backup_vault: Refactor to use keyvaluetags package (#11270)
resource/aws_backup_vault: Refactor to use keyvaluetags package (#11270)

Output from acceptance testing:

```
--- PASS: TestAccAwsBackupVault_basic (19.54s)
--- PASS: TestAccAwsBackupVault_withTags (42.72s)
--- PASS: TestAccAwsBackupVault_withKmsKey (47.87s)
```
terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws