4.x: Update context-root config documentation (#8427)

* update documentation

Signed-off-by: tvallin <thibault.vallin@oracle.com>

docs/src/main/asciidoc/mp/jaxrs/jaxrs-applications.adoc

@@ -64,7 +64,46 @@ in each subclass using the collections in steps (2) and (3) only as defaults, i.
 both return empty sets.
 
 NOTE: Helidon treats `@Path` and `@Provided` as bean-defining annotations but, as stated above,
-`Application` subclasses may require additional annotations depending on the discovery mode.
+`Application` subclasses may require additional annotations depending on the discovery mode
+
+== Setting Application Path
+
+The application path, also known as context root, is the base URI used to serve all resource URIs provided
+by `@Path` annotation. This section describes how to set it with an annotation or configuration file.
+
+When an `Application` subclass is provided, use the `@ApplicationPath`:
+
+[source,java]
+----
+include::{sourcedir}/mp/jaxrs/JaxrsApplicationsSnippets.java[tag=snippet_2, indent=0]
+----
+
+The served resources can be reached through `/my-application/{myResources}` endpoint. It can be overridden
+by configuration file.
+
+Example of custom application path using `.yaml` file:
+
+[source,yaml]
+----
+io.helidon.examples.MyApplication:
+  routing-path:
+    path: "/my-application"
+----
+
+The same configuration works for `.properties` file:
+
+[source,properties]
+----
+io.helidon.examples.MyApplication.routing-path.path=/my-application
+----
+
+If an `Application` is not provided, a _synthetic_ subclass is created and can be configured using
+this property:
+
+[source,properties]
+----
+jakarta.ws.rs.core.Application.routing-path.path=/my-application
+----
 
 == Access to Application Instances
 

docs/src/main/asciidoc/mp/server.adoc

@@ -300,7 +300,8 @@ You can configure `@RoutingPath` to define the path a service is registered on.
 ===== Configuration override of routing path
 
 For each HTTP service class you can define the routing path by specifying a configuration
-option `class-name.routing-path.path`.
+option `class-name.routing-path.path`. The `routing-path` configuration can be applied to Jax-RS application.
+See xref:jaxrs/jaxrs-applications.adoc[Jakarta REST Application] for more information.
 
 Example (YAML) configuration for a class `io.helidon.example.AdminService` that changes the
 routing path to `/management`:

docs/src/main/java/io/helidon/docs/mp/jaxrs/JaxrsApplicationsSnippets.java

@@ -17,6 +17,7 @@
 
 import io.helidon.webserver.http.ServerRequest;
 
+import jakarta.ws.rs.ApplicationPath;
 import jakarta.ws.rs.GET;
 import jakarta.ws.rs.Path;
 import jakarta.ws.rs.core.Application;
@@ -36,4 +37,10 @@ public void get(@Context ServerRequest serverRequest) {
     }
     // end::snippet_1[]
 
+    // tag::snippet_2[]
+    @ApplicationPath("/my-application")
+    public class MyApplication extends Application {
+
+    }
+    // end::snippet_2[]
 }