Support access policies to backup vaults

### Describe the Feature

Support assigning access policies to backup vaults
> With AWS Backup, you can assign policies to backup vaults and the resources they contain. Assigning policies allows you to do things like grant access to users to create backup plans and on-demand backups, but limit their ability to delete recovery points after they're created.

https://docs.aws.amazon.com/aws-backup/latest/devguide/create-a-vault-access-policy.html

### Expected Behavior

Support custom access policies that can be assigned to backup vaults. Terraform resource exists to support this:
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/backup_vault_policy

### Use Case

> Assigning policies allows you to do things like grant access to users to create backup plans and on-demand backups, but limit their ability to delete recovery points after they're created.

https://docs.aws.amazon.com/aws-backup/latest/devguide/create-a-vault-access-policy.html

### Describe Ideal Solution

See expected behaviour

### Alternatives Considered

_No response_

### Additional Context

_No response_