[Feature] Allow for specification of backup policies

[sblack4]

Is your feature request related to a problem? Please describe.

Azure offers recovery services, specifically Azure FileShare Backups, and these are "supported" in terraform

• https://docs.microsoft.com/en-us/azure/backup/azure-file-share-backup-overview
• https://registry.terraform.io/providers/hashicorp/azurerm/1.43.0/docs/resources/backup_container_storage_account
• https://registry.terraform.io/providers/hashicorp/azurerm/1.43.0/docs/resources/backup_policy_file_share
• https://registry.terraform.io/providers/hashicorp/azurerm/1.43.0/docs/resources/backup_protected_file_share
• https://registry.terraform.io/providers/hashicorp/azurerm/1.43.0/docs/resources/backup_container_storage_account

Describe the solution you'd like

I would like the additions in https://github.com/rhythmictech/terraform-azurerm-storage-account/tree/support-fileshare-backups to work

Additional context

Creating a azurerm_backup_protected_file_share through terraform is not currently possible because of hashicorp/terraform-provider-azurerm#6762