[DOCS] Add placeholders for Observability docs (#1216)

* Add placeholders for observability docs

* Restructure headings

docs/en/observability/index.asciidoc

@@ -0,0 +1,11 @@
+:doctype: book
+
+= Observability Guide
+
+include::{docs-root}/shared/versions/stack/{source_branch}.asciidoc[]
+
+include::{docs-root}/shared/attributes.asciidoc[]
+
+include::observability-introduction.asciidoc[]
+
+include::observability-ui.asciidoc[]

docs/en/observability/observability-introduction.asciidoc

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+[[observability-introduction]]
+[role="xpack"]
+== What is Elastic Observability? 
+
+//TODO: Add content
+
+
+[[observability-get-started]]
+== Get started with the {stack}
+
+To get started...
+
+=== Hosted Elasticsearch Service
+
+=== Install the {stack} yourself
+
+=== Run the {stack} on Docker
+
+=== Run the {stack} on Kubernetes
+
+[float]
+==== Step 1: Install {es}
+
+[float]
+==== Step 2: Install {kib}
+
+[[observability-add-data]]
+== Add observability data 
+
+=== Instrument applications
+
+=== Ingest logs
+
+=== Ingest metrics
+
+=== Ingest uptime data

docs/en/observability/observability-ui.asciidoc

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+[[observability-ui]]
+[role="xpack"]
+
+== Monitor observable environments
+
+Displayed on the Observability *Overview* page are a wide variety of chart
+visualizations that provide you with analytical information on what is
+happening within your environments.
+
+The dashboard is comprised of four components to help you make your environments 
+observable; APM, logs, metrics, and uptime. 
+
+=== Services, transactions, and error rates
+
+=== Log rates
+
+=== System metrics
+
+=== Systems availability 
+
+=== Alerts 
+