added code example using HikariCP in Boot 1.x and 2.x (#5007)

* added code example using HikariCP in Boot 1.x and 2.x

* code formatting

spring-4/src/test/java/com/baeldung/connectionpool/ApplicationWithHikariConnectionPool.java

@@ -0,0 +1,12 @@
+package com.baeldung.connectionpool;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class ApplicationWithHikariConnectionPool {
+
+    public static void main(String[] args) {
+        SpringApplication.run(ApplicationWithHikariConnectionPool.class, args);
+    }
+}