feat: Add ability to exclude source fields from query response

[mattref]

Description

Partially inspired by #17003, this change adds the ability to exclude specific document "source" fields from the OpenSearch query response. This change is particularly useful for excluding the embedding_field from query responses, as returning the embeddings for each node (i.e., when the top k is high) can cause quite a lot of allocation (depending on the size of the actual embeddings).

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran uv run make format; uv run make lint to appease the lint gods

[mattref]

Using :latest (which is OpenSearch version 3) causes the following exception on the OpenSearch side when running the tests, thus causing almost all of them to fail:

org.opensearch.index.mapper.MapperParsingException: Failed to parse mapping [_doc]: nmslib engine is deprecated in OpenSearch  and cannot be used for new index creation in OpenSearch from  3.0.0.

[logan-markewich]

Seems like something that needs to be fixed in the future 😞