[Stack Monitoring] Document timeout settings

[miltonhultgren]

Within Metricbeat there is a base timeout of 10 seconds which correlates to the default period setting, this is to avoid calls taking longer than the period to ensure the data is as fresh as the configuration expects.

There are cases where we need to extend the period, such as when an endpoint takes longer to reply for "good" reasons. One example of this is the _cluster/stats endpoint of Elasticsearch for a large cluster state. But, simply setting the period to 20 seconds (for example) isn't enough, since we'll hit the request timeout limit instead.

The below settings can be used to raise the timeout:

- module: elasticsearch
  xpack.enabled: true
  period: 30s
  connect_timeout: 30s
  timeout: 30s

These settings are not well documented (and when to use them is also not documented).

AC

• The different timeout settings and when they might be needed is documented in the documentation for the modules we own
• The internal Knowledgebase entry for support is updated to reference the newly added documenttion

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!