azurerm_api_management - update capacity to allow increasing the apim…

… scalability to 31 (#28427)

Microsoft now allows to sacle up the APIM instance to 31 per region but it is limited by terraform. So with the update in validation it can be updated to 31 using terraform.
MS Docs: https://github.com/MicrosoftDocs/azure-docs/blob/main/includes/api-management-service-limits.md

internal/services/apimanagement/api_management_resource.go

@@ -209,7 +209,7 @@ func resourceApiManagementSchema() map[string]*pluginsdk.Schema {
 						Type:         pluginsdk.TypeInt,
 						Optional:     true,
 						Computed:     true,
-						ValidateFunc: validation.IntBetween(0, 12),
+						ValidateFunc: validation.IntBetween(0, 31),
 					},
 
 					"zones": commonschema.ZonesMultipleOptional(),