USE-257-fulltext

Why these changes are being introduced:
* A new field, fulltext, is needed for TIMDEX sources

How this addresses that need:
* Update opensearch_mappings.json to include fulltext field during searching but exclude it from retrieval
* Add configure_index_settings unit test to confirm fulltext field is present in the loaded mapping
* Update dependencies

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/USE-257

Author: ehanson8