[DOC] Add docs for split event processor

[srikanthjg]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request and all versions that are affected.
New processor: opensearch-project/data-prepper/pull/4166
This will be in Data Prepper 2.7

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[Naarcha-AWS]

#6682