[services] Modify lambda opensearch request to use keyword instead of text

Summary:
This modifies the opensearch modify request to match on keyword instead of text. Term query by default uses a text-based analyzer which causes a mismatch between valid userID queries and results.

This didn't come up during testing before as my test data didn't use uuid for userIDs. This diff fixes this issue by requiring an exact search (using the raw userID) through accessing the keyword field.

Test Plan: Tested on staging. Modify request successfully working

Reviewers: varun

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11179