`connection_idle_timeout` setting missing from standalone and fleet-managed agent docs

This is a performance tuning setting that should appear in both the standalone and Fleet-managed list of settings for the Agent Elasticsearch output.

Sample agent config file from Fleet 8.12.0 (note that some settings have prefixes added for 8.12.1).
```
id: ae050009-40b8-437f-95ce-93010ad5910a
revision: 6
outputs:
a1803e62-1979-4609-ad6a-fe0ec7299794:
type: elasticsearch
bulk_max_size: 1600
worker: 1
queue.mem.events: 3200
queue.mem.flush.min_events: 1600
queue.mem.flush.timeout: 10s
compression_level: 1
connection_idle_timeout: 3s
hosts:
- 'http://localhost:9200'
username: '${ES_USERNAME}'
password: '${ES_PASSWORD}'
preset: custom
default:
type: elasticsearch
hosts:
- 'https://95bcf2d63970461fab4201b9490dfb89.us-central1.gcp.cloud.es.io:443'
username: '${ES_USERNAME}'
password: '${ES_PASSWORD}'
preset: balanced
```

I believe it's this setting in Filebeat:
https://www.elastic.co/guide/en/beats/filebeat/current/logstash-output.html#_timeout_2