Fix S360 item for FSPG swagger by adding default value to backupRetentionDays and maintenanceWindow (Azure#16502)

* Changed FSPG RestartParameter.failoverMode from string to enum for API 2021-06-01, 2021-06-01-preview, and 2021-06-15-privatepreview

* Change enum first letter to lower case

* Change to upper case

* Fix S360 bugs for swagger FSPG 2020-02-14-preview, 2021-06-01-preview and 2021-06-01 APIs

* Fix S360 item by adding default value to backupRetentionDays and maintenanceWindow

Author: xunsun-commits

specification/postgresql/resource-manager/Microsoft.DBforPostgreSQL/preview/2021-06-01-preview/postgresql.json

@@ -1423,6 +1423,7 @@
         },
         "maintenanceWindow": {
           "$ref": "#/definitions/MaintenanceWindow",
+          "default": null,
           "description": "Maintenance window properties of a server.",
           "x-ms-mutability": [
             "update",
@@ -1525,6 +1526,7 @@
         },
         "maintenanceWindow": {
           "$ref": "#/definitions/MaintenanceWindow",
+          "default": null,
           "description": "Maintenance window properties of a server.",
           "x-ms-mutability": [
             "update",
@@ -1631,6 +1633,7 @@
         "backupRetentionDays": {
           "type": "integer",
           "format": "int32",
+          "default": 7,
           "description": "Backup retention days for the server."
         },
         "geoRedundantBackup": {

specification/postgresql/resource-manager/Microsoft.DBforPostgreSQL/stable/2021-06-01/postgresql.json

@@ -1423,6 +1423,7 @@
         },
         "maintenanceWindow": {
           "$ref": "#/definitions/MaintenanceWindow",
+          "default": null,
           "description": "Maintenance window properties of a server.",
           "x-ms-mutability": [
             "update",
@@ -1525,6 +1526,7 @@
         },
         "maintenanceWindow": {
           "$ref": "#/definitions/MaintenanceWindow",
+          "default": null,
           "description": "Maintenance window properties of a server.",
           "x-ms-mutability": [
             "update",
@@ -1631,6 +1633,7 @@
         "backupRetentionDays": {
           "type": "integer",
           "format": "int32",
+          "default": 7,
           "description": "Backup retention days for the server."
         },
         "geoRedundantBackup": {