Vipinhas/add min capacity clusters (#15290)

* removing read only property, no longer in use - NOT a breaking change

* add min value for LA cluster capacity reservation

Author: vipinhas

specification/operationalinsights/resource-manager/Microsoft.OperationalInsights/stable/2021-06-01/Clusters.json

@@ -635,10 +635,11 @@
         },
         "capacityReservationLevel": {
           "readOnly": true,
-          "description": "The capacity reservation level for this cluster",
+          "description": "The capacity reservation level for this cluster in GB",
           "type": "integer",
           "format": "int32",
           "enum": [
+            500,
             1000,
             2000,
             5000