[8.16](backport #41570) Metricbeat: add configurable failure threshold before reporting streams as degraded

Proposed commit message

Add configurable failure threshold before reporting streams as degraded

With this change it is possible to configure a threshold for the number of consecutive errors that may happen while fetching metrics for a given stream before the stream gets marked as DEGRADED. To configure such threshold, add a "failure_threshold": <n> to a module configuration block. Depending on the value of <n> the threshold will be configured in different ways:

n == 0: status reporting for the stream has been disabled, the stream will never become DEGRADED no matter how many errors are encountered while fetching metrics
n==1 or failure_threshold not specified: backward compatible behavior, the stream will become DEGRADED at the first error encountered
n > 1: stream will become DEGRADED after at least n consecutive errors have been encountered

When a fetch operation completes without errors the consecutive errors counter is reset and the stream is set to HEALTHY.

Checklist

[x] My code follows the style guidelines of this project
[x] I have commented my code, particularly in hard-to-understand areas
[x] I have made corresponding changes to the documentation
~~[ ] I have made corresponding change to the default configuration files~~
[x] I have added tests that prove my fix is effective or that my feature works
~~[ ] I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.~~

Disruptive User Impact

No disruptive user impact since not specifying the new configuration key maintains the previous behavior

elastic / beats