[REQUEST]: Add getting started section and reorganize content under it

[dedemorton]

What documentation page is affected

Pages under Send Data to Elasticsearch.

What change would you like to see?

As part of spacetime, the obs-docs team is making improvements to the Information Architecture of the Observability Guide. This issue tracks the work needed to convert the existing "Send Data to Elasticsearch" to a section called "Get started." Specifically we need to:

• Merge content from Ingest logs and metrics and Spin up the Elastic Stack, fix links
• Remove on-prem instructions
  • Verify that the on-prem instructions and prereqs are fully documented in the Fleet/Agent guide. Opened issue because these prereqs need to be validated: Verify that prereqs for running Elastic Agent and Fleet with self-managed cluster are fully documented ingest-docs#177
• Move ESF content (see Remove Elastic Serverless Forwarder source files from the obs guide (main branch only) #2853)
• Delete Beats content, set up redirects
  • Move intro and deployment considerations to the Heartbeat docs because it's not covered there. Created an issue to track this: Add deployment considerations to the Heartbeat docs beats#35255
• Update Observability content in Welcome to Elastic book. Opened https://github.com/elastic/tech-content/pull/329,
• Clean up/delete all source files that were removed (after confirming that the content is fully covered elsewhere).
• Write overview content for getting started section.

Additional info

No response

[dedemorton]

Closed by #2880