Fix health and metrics URLs. Mention health returns 204 (helidon-io#8160)

Author: barchetta

docs/se/guides/quickstart.adoc

@@ -104,19 +104,21 @@ Helidon provides built-in support for health and metrics endpoints.
 [source,bash]
 .Health
 ----
-curl -s -X GET http://localhost:8080/health
+curl -sv -X GET http://localhost:8080/observe/health
 ----
 
+Notice we use the `-v` option to curl so that you can see that the health endpoint returns 204 (No Content) by default.
+
 [source,bash]
 .Metrics in Prometheus Format
 ----
-curl -s -X GET http://localhost:8080/metrics
+curl -s -X GET http://localhost:8080/observe/metrics
 ----
 
 [source,bash]
 .Metrics in JSON Format
 ----
-curl -H 'Accept: application/json' -X GET http://localhost:8080/metrics
+curl -H 'Accept: application/json' -X GET http://localhost:8080/observe/metrics
 ----
 
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