Modify the search response to exclude the attachments from the response

[chouinar]

Summary

We don't need the attachments in the search results, and parsing the large text responses would be a lot of extra parsing, so we shouldn't have OpenSearch return them.

This can be done by adding _source_excludes=field1,field2 to the query we send to OpenSearch (_search_excludes is also a param that the search client we use takes in).

Acceptance criteria

1. Modified the search method of our opensearch client to pass through an optional excludes param
2. Modified our search API to set the attachments field to be excluded