unsuitable repeat_interval samples in alertmanager

Description of problem:

https://docs.openshift.com/container-platform/4.11/monitoring/managing-alerts.html#applying-custom-alertmanager-configuration_managing-alerts
https://access.redhat.com/documentation/en-us/openshift_container_platform/4.11/html/monitoring/managing-alerts#applying-custom-alertmanager-configuration_managing-alerts

A sample "Applying a custom Alertmanager configuration" looks like this:

alertmanager.yaml
```
global:
  resolve_timeout: 5m
route:
  group_wait: 30s
  group_interval: 5m         <== here
  repeat_interval: 12h
  receiver: default
  routes:
  - match:
      alertname: Watchdog
    repeat_interval: 5m      <== here
    receiver: watchdog
... snip ...
```

 This setting has the same value for group_interval and repeat_interval and is known to cause race conditions. So this actually sends alerts randomly at 5 or 10 minutes.This creates unnecessary confusion for customers. Please update avoid race conditions.

Version-Release number of selected component (if applicable):

4.ll

Actual results:

  - match:
      alertname: Watchdog
    repeat_interval: 5m
    receiver: watchdog 

This sample alerts in 5 or 10 minutes randomly.

Expected results:

Need a sample that correctly alerts me every 5 minutes.

We know from some investigate and customer feedback that neither of the following patterns will trigger alerts exactly every 5 minutes.

  - match:
      alertname: Watchdog
    repeat_interval: 1h
    receiver: watchdog 

and

  - match:
      alertname: Watchdog
    group_wait: 30s
    group_interval: 1m
    repeat_interval: 5m
    receiver: watchdog 

• If this is an implementation-based limitation, there should at least be a warning in the documentation.

Additional info:

Need QE that make sure race conditions are not occurring