fix H1s per seo suggestions (elastic#3081)

fix H1 per SEO
add navigation_titles to retain nav titles as before

---------

Co-authored-by: Liam Thompson <[email protected]>

Author: ketkee-aryamane

reference/data-analysis/machine-learning/machine-learning-functions.md

@@ -1,11 +1,12 @@
 ---
 mapped_pages:
   - https://www.elastic.co/guide/en/machine-learning/current/ml-functions.html
+navigation_title: Function reference
 products:
   - id: machine-learning
 ---
 
-# Function reference [ml-functions]
+# Function reference for Elastic {{ml} [ml-functions]
 
 The {{ml-features}} include analysis functions that provide a wide variety of flexible ways to analyze data for anomalies.
 

reference/fleet/index.md

@@ -5,13 +5,14 @@ mapped_pages:
   - https://www.elastic.co/guide/en/kibana/current/fleet.html
   - https://www.elastic.co/guide/en/fleet/current/fleet-overview.html
   - https://www.elastic.co/guide/en/fleet/current/index.html
+navigation_title: Fleet and Elastic Agent
 products:
   - id: cloud-serverless
   - id: fleet
   - id: kibana
 ---
 
-# Fleet and Elastic Agent [fleet-and-elastic-agent]
+# {{fleet}} and {{elastic-agent}} overview [fleet-and-elastic-agent]
 
 % Internal links rely on the following IDs being on this page (e.g. as a heading ID, paragraph ID, etc):
 $$$package-registry-intro$$$

reference/observability/fields-and-object-schemas.md

@@ -3,6 +3,7 @@ mapped_pages:
   - https://www.elastic.co/guide/en/observability/current/fields-reference.html
   - https://www.elastic.co/guide/en/observability/current/metrics-app-fields.html
   - https://www.elastic.co/guide/en/serverless/current/observability-infrastructure-monitoring-required-fields.html
+navigation_title: Fields and object schemas
 applies_to:
   stack: all
   serverless: all
@@ -11,7 +12,7 @@ products:
   - id: cloud-serverless
 ---
 
-# Fields and object schemas [fields-reference]
+# Fields and object schemas for {{observability}} [fields-reference]
 
 This section lists Elastic Common Schema (ECS) fields the Infrastructure apps use to display data.
 

reference/security/fields-and-object-schemas/index.md

@@ -1,6 +1,7 @@
 ---
 mapped_pages:
   - https://www.elastic.co/guide/en/security/current/security-ref-intro.html
+navigation_title: Fields and object schemas
 applies_to:
   stack: all
   serverless:
@@ -9,7 +10,7 @@ products:
   - id: security
 ---
 
-# Fields and object schemas [security-ref-intro]
+# Fields and object schemas for {{elastic-sec}} [security-ref-intro]
 
 This reference section provides details on the fields {{elastic-sec}} uses to display data in the UI and {{elastic-sec}} JSON object schemas: