Add links to ILM docs in agent tutorials and integrations main page (#3127)

In a review of the ILM docs it was requested that we add links to those
docs from various quickstarts, etc.

As part of that, this PR:

- Adds a link at the end of the two [standalone agent nginx
tutorials](https://www.elastic.co/docs/reference/fleet/example-standalone-monitor-nginx):
<img width="318" height="182" alt="ingest"
src="https://github.com/user-attachments/assets/96961bdb-8366-42cf-84f4-4ffd3c794af9"
/>

- Adds a tip at the bottom of the main "Manage Elastic Agent
Integrations" page.
<img width="576" height="114" alt="ingest2"
src="https://github.com/user-attachments/assets/bdd46b27-0496-424b-b9d7-3edd1afb4720"
/>

Please see previews:
- [Example: Use standalone Elastic Agent with Elastic Cloud Hosted to
monitor
nginx](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/3127/reference/fleet/example-standalone-monitor-nginx#_whats_next_2)
- [Example: Use standalone Elastic Agent with Elastic Cloud Serverless
to monitor
nginx](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/3127/reference/fleet/example-standalone-monitor-nginx-serverless#_whats_next)
- [Manage Elastic Agent
Integrations](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/3127/reference/fleet/manage-integrations)
(at the bottom)

Rel: #1568

Author: kilfoyle

reference/fleet/example-standalone-monitor-nginx-serverless.md

@@ -315,3 +315,4 @@ Congratulations! You have successfully set up monitoring for nginx using standal
 
 * Learn more about [{{fleet}} and {{agent}}](/reference/fleet/index.md).
 * Learn more about [{{integrations}}](integration-docs://reference/index.md).
+* Learn how to manage your [data lifecycle](/manage-data/lifecycle.md).

reference/fleet/example-standalone-monitor-nginx.md

@@ -314,3 +314,4 @@ Congratulations! You have successfully set up monitoring for nginx using standal
 
 * Learn more about [{{fleet}} and {{agent}}](/reference/fleet/index.md).
 * Learn more about [{{integrations}}](integration-docs://reference/index.md).
+* Learn how to manage your [data lifecycle](/manage-data/lifecycle.md).

reference/fleet/manage-integrations.md

@@ -47,15 +47,6 @@ The **Integrations** app in {{kib}} needs access to the public {{package-registr
 
 ::::
 
-
-
-
-
-
-
-
-
-
-
-
-
+:::{tip}
+Once you've started using integrations to ingest data, you can customize how that data is managed over time. Refer to [Index lifecycle management](/reference/fleet/data-streams.md#data-streams-ilm) to learn more.
+:::