Search Transcription Text from Browse Hearings Page

## Problem

On our Browse Hearings page, we currently don't include the transcription text itself as a searchable field (e.g. so if a user wants to find all hearings that discuss "Healthcare Subsidies", there is no easy way to do so).

We have all the transcription text in Firestore already, so we should be able to add these fields to our Typesense index and include them as searchable (but not filterable) fields.

## Success Criteria
- [ ] Add `transcriptionText` as a new field to the Hearings Typesense index
- [ ] Add `transcriptionText` as an option for the search in the main Search bar on the Browse Hearings page

Locate the Hearings Typesense indexing flow and the main Search bar on the Browse Hearings page; trace how transcription text is loaded from Firestore into the index. Done means the Hearings index contains a non-filterable transcriptionText field and searches from the Browse Hearings page can match transcription text.

Written by the indexing model from the issue text.