Suggest chunking for large ELSER fields

[seanstory]

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[github-actions]

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[mergify]

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

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[seanstory]

I don't seem to have permission to modify labels. This should probably get backported. CC @leemthompo I'm hoping you can shepherd this? 🙏 (couldn't explicitly add you as a reviewer, either)

[szabosteve]

Thank you for this addition! LGTM!