[FEATURE] Require, standardize and import descriptions.

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Is your feature request related to a problem?

I think we will end up generating documentation from spec into https://github.com/opensearch-project/documentation-website. That site has a lot of inconsistencies around wording, defaults, or quoting. See opensearch-project/documentation-website#7660 for an example.

What solution would you like?

• Import descriptions from https://github.com/opensearch-project/documentation-website.
• Require a description: field for all structures.
• Lint the descriptions. We already check spelling, but ensure that there are no decorative quotes (see Fix quotes in descriptions. #402). No text that says "Default is blah", instead use a default: field. Consistently capitalize sentences and add periods at the end. Have the same tense.
• Lint the descriptions of tests.

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With #620 we check description styles (3) and (4).