[DOC] Add documentation for variable_count_threshold and frequency_threshold_percentage on patterns

[paulstn]

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.

I would like more documentation on variable_count_threshold and frequency_threshold_percentage within the patterns command, for when method=brain.

Ideally, I'd like to have enough documentation to where I wouldn't have to look within code to know exactly how these parameters would interact with the patterns command results. i.e. how it would potentially transform my data.

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

3.1-3.3

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

[songkant-aws]

Will do this one

[penghuo]

@songkant-aws could we close this PR with #4402

[songkant-aws]

@penghuo Yes, I think we can close it with #4402