Add troubleshooting for dynamic mapping exceptions

What does this MR do and why?

Related to #408214 (closed)

Add documentation section for troubleshooting Advanced Search indexing. The strict_dynamic_mapping_exception errors in the logs are common when migrations have not completed before a major upgrade. I think it's important to have this error documented for self managed customers and support team members.

Screenshots or screen recordings

N/A

How to set up and validate locally

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