Add ElasticsearchOptions.UseClusterHealth option

By default the option is false, meaning it will use ping as it was
previously doing. If the user wants advanced health check they can
call this method which will instruct ElasticsearchHealthCheck to use
the Cluster Health API instead. See parent commit for more information.

src/HealthChecks.Elasticsearch/ElasticsearchHealthCheck.cs

@@ -48,26 +48,39 @@ public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context
                     }
                 }
 
-                var healthResult = await lowLevelClient.Cluster.HealthAsync(ct: cancellationToken);
-
-                if (healthResult.ApiCall.HttpStatusCode != 200)
+                if (_options.CheckClusterHealth)
                 {
-                    return new HealthCheckResult(context.Registration.FailureStatus);
-                }
 
-                switch (healthResult.Status.ToString())
-                {
-                    case "green":
-                        return HealthCheckResult.Healthy();
+                    var healthResult = await lowLevelClient.Cluster.HealthAsync(ct: cancellationToken);
+
+                    if (healthResult.ApiCall.HttpStatusCode != 200)
+                    {
+                        return new HealthCheckResult(context.Registration.FailureStatus);
+                    }
 
-                    case "yellow":
-                        return HealthCheckResult.Degraded();
+                    switch (healthResult.Status.ToString())
+                    {
+                        case "green":
+                            return HealthCheckResult.Healthy();
+
+                        case "yellow":
+                            return HealthCheckResult.Degraded();
+
+                        case "red":
+                            return HealthCheckResult.Unhealthy();
+                    }
 
-                    case "red":
-                        return HealthCheckResult.Unhealthy();
+                    return HealthCheckResult.Unhealthy();
                 }
+                else
+                {
+                    var pingResult = await lowLevelClient.PingAsync(ct: cancellationToken);
+                    var isSuccess = pingResult.ApiCall.HttpStatusCode == 200;
 
-                return HealthCheckResult.Unhealthy();
+                    return isSuccess
+                        ? HealthCheckResult.Healthy()
+                        : new HealthCheckResult(context.Registration.FailureStatus);
+                }
             }
             catch (Exception ex)
             {