Update field mapping for 'rights.description' to index values as keywords

Why these changes are being introduced:
* This change is required in order to perform aggregations on the 'description'
property of the 'rights' field. More specifically, this work is to enable
filtering based on "Access to files" and support the updates to the TIMDEX
data model in the PR: MITLibraries/transmogrifier#114

How this addresses that need:
* Update config to convert 'rights.description' to a multifield that indexes
the value as a "keyword" in a similarly named subfield (i.e., 'description.keyword')

Side effects of this change:
* None

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/GDT-138

Author: jonavellecuerdo

README.md

@@ -115,7 +115,7 @@ OPENSEARCH_REQUEST_TIMEOUT=
 # The ingest process logs the # of records indexed every nth record. Set this env variable to any integer to change the frequency of logging status updates. Can be useful for development/debugging. Defaults to 1000 if not set.
 STATUS_UPDATE_INTERVAL= 
 
-# If using a local Docker OpenSearch instance, this isn't needed. Otherwise set to OpenSearch instance endpoint without the http schem (e.g., "search-timdex-env-1234567890.us-east-1.es.amazonaws.com"). Can also be passed directly to the CLI via the `--url` option.
+# If using a local Docker OpenSearch instance, this isn't needed. Otherwise set to OpenSearch instance endpoint without the http scheme (e.g., "search-timdex-env-1234567890.us-east-1.es.amazonaws.com"). Can also be passed directly to the CLI via the `--url` option.
 TIMDEX_OPENSEARCH_ENDPOINT= 
 
 # If set to a valid Sentry DSN, enables Sentry exception monitoring This is not needed for local development.

config/opensearch_mappings.json

@@ -339,7 +339,12 @@
         "type": "nested",
         "properties": {
           "description": {
-            "type": "text"
+            "type": "text",
+            "fields": {
+              "keyword": {
+                "type": "keyword"
+              }
+            }
           },
           "kind": {
             "type": "keyword",