Add default value for health check expiry (#3345)

add default for health check expiry

src/Microsoft.Health.Dicom.Blob/Utilities/ExternalBlobDataStoreConfiguration.cs

@@ -23,7 +23,7 @@ internal class ExternalBlobDataStoreConfiguration
     public string HealthCheckFilePath { get; set; }
 
     [Range(typeof(TimeSpan), "00:01:00", "1.00:00:00", ConvertValueInInvariantCulture = true, ParseLimitsInInvariantCulture = true)]
-    public TimeSpan HealthCheckFileExpiry { get; set; }
+    public TimeSpan HealthCheckFileExpiry { get; set; } = TimeSpan.FromMinutes(5);
 
     /// <summary>
     /// A path which is used to store blobs along a specific path in a container, serving as a prefix to the