[bs-120] Support for groovy templates

* Added GroovyTemplate.template() utility and static import in webapp CLI, so

        @RequestMapping("/")
        @ResponseBody
        String home(Model model) {
           template "home.html", model
        }

    renders the template in /templates/home.html

[Fixes #49832753]

spring-bootstrap-cli/src/test/java/org/springframework/bootstrap/cli/SampleIntegrationTests.java

@@ -92,6 +92,13 @@ public class SampleIntegrationTests {
 		assertTrue("Wrong output: " + output, output.contains("Hello World"));
 	}
 
+	@Test
+	public void templateSample() throws Exception {
+		start("samples/template.groovy");
+		String output = getOutput();
+		assertTrue("Wrong output: " + output, output.contains("Hello World!"));
+	}
+
 	@Test
 	public void jobSample() throws Exception {
 		start("samples/job.groovy", "foo=bar");

spring-bootstrap-cli/src/test/resources/templates/test.txt

@@ -0,0 +1 @@
+Hello ${message}!