Add SpringApplicationBuilder

Builder for SpringApplication and ApplicationContext instances with
convenient fluent API and context hierarchy support. Simple example
of a context hierarchy:

   new SpringApplicationBuilder(ParentConfig.class)
               .child(ChildConfig.class).run(args);

Another common use case is setting default arguments, e.g.
active Spring profiles, to set up the environment for an application:

     new SpringApplicationBuilder(Application.class).profiles("server")
 		.defaultArgs("--transport=local").run(args);

If your needs are simpler, consider using the static convenience
methods in SpringApplication instead.

[#49703716] [bs-116] Parent context for some beans maybe?

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/EndpointWebMvcChildContextConfiguration.java

@@ -40,7 +40,7 @@ import org.springframework.web.servlet.HandlerAdapter;
 import org.springframework.web.servlet.HandlerMapping;
 
 /**
- * Configuration for triggered from {@link EndpointWebMvcAutoConfiguration} when a new
+ * Configuration triggered from {@link EndpointWebMvcAutoConfiguration} when a new
  * {@link EmbeddedServletContainer} running on a different port is required.
  * 
  * @see EndpointWebMvcAutoConfiguration