#95641 upgraded Jackson to version 2.15.0.  One of the fixes in this is https://github.com/FasterXML/jackson-core/issues/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`](https://github.com/elastic/elasticsearch/files/11453951/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.
libs/x-content/impl/src/main/java/org/elasticsearch/xcontent/provider/json/JsonXContentImpl.java
public static XContentBuilder getContentBuilder() throws IOException {
        return XContentBuilder.builder(jsonXContent);
    }
    private static final JsonFactory jsonFactory;
    public static final XContent jsonXContent;
    public static final XContent jsonXContent() {
        return jsonXContent;
    }
    static {
        jsonFactory = new JsonFactory();
        jsonFactory.configure(JsonGenerator.Feature.QUOTE_FIELD_NAMES, true);
        jsonFactory.configure(JsonParser.Feature.ALLOW_COMMENTS, true);
        jsonFactory.configure(JsonFactory.Feature.FAIL_ON_SYMBOL_HASH_OVERFLOW, false); 
        
        jsonFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_JSON_CONTENT, false);
        jsonFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, true);
        jsonFactory.configure(JsonParser.Feature.USE_FAST_DOUBLE_PARSER, true);
        jsonXContent = new JsonXContentImpl();
    }
    private JsonXContentImpl() {}
    @Override
    public XContentType type() {
        return XContentType.JSON;
    }
    @Override
    public byte streamSeparator() {
        return '\n';
    }