[DOCS] Java REST Client: document `setMaxConnPerRoute()` + `setMaxConnTotal()`

[n0othing]

The Java REST Client exposes three tunable parameters:

• Thread Count
• Max Connections Per Route (setMaxConnPerRoute())
• Max Connections Total (setMaxConnTotal())

We document how to adjust the thread count [1] but not connections per route / total and it'd be helpful to cover these for users.

Worth noting that In scenarios where the client is communicating to an Elasticsearch cluster via a proxy (e.g an ECE backed cluster), the proxy endpoint is treated as a single route-- increasing connections per + total offers a dramatic performance boost for concurrent requests.

[1] https://www.elastic.co/guide/en/elasticsearch/client/java-rest/current/_number_of_threads.html

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[rahst12]

The URL changed to: https://www.elastic.co/guide/en/elasticsearch/client/java-rest/7.13/_number_of_threads.html

This documentation is still really useful for ECE paid subscribers.