Enhance logic for splitting large payload requests by querying http.max_content_length from Elasticsearch

[rodrigc]

Describe the enhancement:

In this discussion thread: https://discuss.elastic.co/t/fix-to-libbeats-to-split-bulk-requests-which-are-too-large-not-working-in-elastic-agent-8-9-0/342136

I raised the point that the GET _cluster/settings API returns http.max_content_length.

My request is that beats and elastic-agent query http.max_content_length from Elasticsearch,
and use this value as part of setting the size of the payload in POST _bulk calls to the server.

A lot of work as gone into PR 34911: Split large batches on error instead of dropping them, but
I think querying http.max_content_length from the server could enhance this logic and make it more robust,
for very large payloads

Enhancement Request: 19624