Add link to the APM OTel guide in the ingest overview (#444)

@colleenmcginnis In the `otel-documentation` Slack channel we have a
request to mention the OTel APM guide somewhere in the ingest overview
content. There are many Observability guides so it might not be ideal to
link directly to just this one, but then we don't really have mention of
OTel elsewhere in the top-level ingestion content, so it does seem worth
highlighting.

This would add a link to the "[Ingesting data for Elastic
solutions](https://github.com/elastic/docs-content/blob/main/manage-data/ingest/ingesting-data-for-elastic-solutions.md)"
page.

Please let me know what you think.

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<img width="807" alt="Screenshot 2025-02-13 at 11 03 16 AM"
src="https://github.com/user-attachments/assets/f20e6395-50ac-44fd-be91-0e3709f1519c"
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Author: kilfoyle

manage-data/ingest/ingesting-data-for-elastic-solutions.md

@@ -59,6 +59,8 @@ With [Elastic Observability](https://www.elastic.co/observability), you can moni
     * [Monitor hosts with {{agent}} ({{serverless-short}})](https://docs.elastic.co/serverless/observability/quickstarts/monitor-hosts-with-elastic-agent)
     * [Monitor your K8s cluster with {{agent}} ({{serverless-short}})](https://docs.elastic.co/serverless/observability/quickstarts/k8s-logs-metrics)
 
+* [Use OpenTelemetry with APM](../../solutions/observability/apps/use-opentelemetry-with-apm.md)
+
 
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