Pre-release 8.8.0 cannot work with string fields longer than 5000000 characters

[droberts195]

#95641 upgraded Jackson to version 2.15.0. One of the fixes in this is FasterXML/jackson-core#863. This new limit of 5000000 characters for a string field then applies to strings in Elasticsearch documents.

To reproduce:

1. ./gradlew run
2. Download big_a.zip
3. unzip big_a.zip
4. curl -u elastic:password http://localhost:9200/my-index/_doc/1 -X PUT -d @big_a.json -H 'Content-Type: application/json'

The response is:

{"error":{"root_cause":[{"type":"document_parsing_exception","reason":"[1:20] failed to parse: String length (5043368) exceeds the maximum length (5000000)"}],"type":"document_parsing_exception","reason":"[1:20] failed to parse: String length (5043368) exceeds the maximum length (5000000)","caused_by":{"type":"stream_constraints_exception","reason":"String length (5043368) exceeds the maximum length (5000000)"}},"status":400}

I think this is a blocker for release of 8.8.0 because people will have indexed docs in older versions that have strings longer than 5000000 characters, and they won't be able to work with them in 8.8.0 unless we do something about this problem.

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)