[DOC] Add split processor documentation

[vagimeli]

Description

Closes content gap

Issues Resolved

#4647

Checklist

• [x] By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[vagimeli]

@hdhalter We need a dev to take the first pass at drafting this content. I can support them in refining the content and getting it through the documentation process. The ingest processor template is provided with this PR, so it should help the dev get started. Thanks!

[vagimeli]

@gaobinlong This PR is ready for your review at your availability. Thank you for all your technical reviews on these topics!

[vagimeli]

@natebower Thank you for the thorough review. I've accepted your edits. Will you approve for merging? This is part of the series that I opened PRs and co-authored with dev, but can't approve. Thank you.