[DOC] Document _source in _search

[dblock]

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.

The documentation in https://opensearch.org/docs/latest/api-reference/search/ for _source looks incorrect. The field accepts booleans, an array of fields, and an includes: or excludes: filter at the very least.

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

2.x

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

opensearch-project/opensearch-api-specification#430