feat: add health check example

examples/healthcheck/README.md

@@ -0,0 +1,13 @@
+# Health check for GreptimeDB
+
+## Run Health Check
+
+```go
+go run main.go
+```
+
+Output:
+
+```log
+2024/09/11 12:13:11 the greptimedb is health
+```

examples/healthcheck/main.go

@@ -36,9 +36,9 @@ func init() {
 }
 
 func main() {
-	resp, err := client.HealthCheck(context.TODO())
+	_, err := client.HealthCheck(context.Background())
 	if err != nil {
-		log.Println(err)
+		log.Println("failed to health check:", err)
 	}
-	log.Println("health check response:", resp)
+	log.Println("the greptimedb is health")
 }