[Reference] Revisit Observability landing page (#1320)

This PR updates the Observability landing page.
Relates to #1303

Author: alaudazzi

reference/observability/index.md

@@ -8,11 +8,12 @@ mapped_pages:
 ---
 # Observability
 
-% TO-DO: Add links to "What is Elastic Observability?"%
+This section contains reference information for Elastic Observability features, including:
 
-This section contains field reference information Infrastructure app fields.
+* [Fields and object schemas](/reference/observability/fields-and-object-schemas.md)
 
-You can use these APIs to interface with Elastic Observability features:
+To learn more about Observability features and how to get started, refer to [Elastic Observability](/solutions/observability.md).
+To interface with Elastic Observability features, you can use the following APIs:
 
 * [Observability Intake Serverless APIs](https://www.elastic.co/docs/api/doc/observability-serverless)
 * [Service level objectives](https://www.elastic.co/docs/api/doc/kibana/group/endpoint-slo)