[Serverless] Adds auto import page

[benironside]

Addresses #5272 by adding a page for the "auto import" feature to the "ingest" section of serverless docs. ESS version to follow.

Preview: Auto import

[github-actions]

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[mergify]

This pull request does not have a backport label. Could you fix it @benironside? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• v7.x is the label to automatically backport to the 7.x branch.
• v7./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticdocs]

🚀 Built elastic-dot-co-docs-preview-docs successfully!

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• Built with commit 804eb69

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[jmikell821]

Left a few comments for your review. Thanks for pulling it together! Would like to review again after other feedback with fresh eyes, in case I missed a few things.

[joepeeples]

Great content! Hopefully these suggestions are helpful and easy to implement.

[natasha-moore-elastic]

A few minor suggestions, otherwise looks good!

[jmikell821]

Just a few comments to tidy this up, then it'll be good to go! Feel free to have another team member give it the once-over before merging. Thank you!

[joepeeples]

🔥 🔥 🔥