[ReleasePR recoveryservicesbackup] Migrate to net track2 for some res…

…ource-manager readmes batch 3 (#2628)

Create to sync Azure/azure-rest-api-specs#21241
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...azure-sdk:sdkAuto/recoveryservicesbackup?expand=1)

schemas/2022-03-01/Microsoft.RecoveryServices.Backup.json

@@ -1021,7 +1021,8 @@
             {
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
-          ]
+          ],
+          "description": "Type of backup policy type."
         },
         "retentionPolicy": {
           "oneOf": [