Custom workspace backup policies

Is your feature request related to a problem? Please describe.
Backup policies in the base workspace are currently hard coded and non-configurable.

Describe the solution you'd like
I'd like to have the option to define custom backup policies when deploying a workspace.

Describe alternatives you've considered
Modifying the template to add more backup policies and a drop down to select them.
A separate file defining custom backup policies that could be read by the terraform

Additional context
templates/workspaces/base/terraform/backup/backup.tf

resource "azurerm_backup_policy_vm" "vm_policy" {
  name                = local.vm_backup_policy_name
  resource_group_name = var.resource_group_name
  recovery_vault_name = azurerm_recovery_services_vault.vault.name


  timezone = "UTC"

  backup {
    frequency = "Daily"
    time      = "22:00"
  }

  retention_daily {
    count = 14
  }

  retention_weekly {
    count    = 4
    weekdays = ["Sunday"]
  }

  retention_monthly {
    count    = 12
    weekdays = ["Monday"]
    weeks    = ["First"]
  }

  retention_yearly {
    count    = 2
    months   = ["December"]
    weekdays = ["Sunday"]
    weeks    = ["Last"]
  }

  depends_on = [
    azurerm_recovery_services_vault.vault
  ]


}

resource "azurerm_backup_policy_file_share" "file_share_policy" {
  name                = local.fs_backup_policy_name
  resource_group_name = var.resource_group_name
  recovery_vault_name = azurerm_recovery_services_vault.vault.name

  timezone = "UTC"

  backup {
    frequency = "Daily"
    time      = "23:00"
  }

  retention_daily {
    count = 14
  }

  retention_weekly {
    count    = 4
    weekdays = ["Sunday"]
  }

  retention_monthly {
    count    = 12
    weekdays = ["Monday"]
    weeks    = ["First"]
  }

  retention_yearly {
    count    = 2
    months   = ["December"]
    weekdays = ["Sunday"]
    weeks    = ["Last"]
  }

  depends_on = [
    azurerm_recovery_services_vault.vault
  ]

}

Start with templates/workspaces/base/terraform/backup/backup.tf and review how the VM and file-share policies are currently hard coded. Trace how workspace deployment inputs reach these Terraform resources, then determine how custom policy definitions should be supplied and selected. Done means deployments can define and use custom backup policies without editing the base template.