[DOC] Add default text_docs input pre/post processor docs in ml-commons

[zane-neo]

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.
Per this issue and this PR in ml-commons, we need to add the documentation to ml-commons plugin to let user know the default processors and how to use them in remote inference case correctly.

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

[hdhalter]

@zane-neo - Is this feature going in 2.11? It's on the project roadmap, but wanted to confirm. Thanks.

[kolchfa-aws]

It will be going into 2.11 opensearch-project/ml-commons#1397