[DOC] Add documentation for the max_ngram_diff when migrating from older versions of Elasticsearch

[peternied]

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.
In modern versions of OpenSearch the max_ngram_diff must be included on any ngram tokenizer/filters with more than 1 distance between min and max. We should document this as a breaking change that customers can work around

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
All versions

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
See related pull request [1]

• [1] Add transformation for adding max_ngram_diff when needed opensearch-migrations#1927