munin-limits: Support delayed alerting

[cweiske]

Is your feature request related to a problem? Please describe.
I am using the http response code plugin to monitor website availability. Internet is not always stable, so sometimes I get an "site offline" notification, and 5 minutes later a "site is back online".

The same happens for DNS performance monitoring with the dnsperftest plugin. Sometimes a DNS server's response time is over my limit of 0.3s, but 5 minutes later it's ok again.

I only want to be notified when the problem persists, not about flukes.

Describe the solution you'd like
In addition to warning and critical plugin configuration settings, I'd like to see a new setting that defines the minimum number of repeated times the error/warning must occur before I get notified.

Describe alternatives you've considered
None.

Additional context

21.06.25, 11:30
home.cweiske.de :: dojo :: DNS server resonse times
	WARNINGs: 2a00:f826:8:2::195 is 0.31 (outside range [:0.300]).
	OKs: 2a00:f826:8:1::254 is 0.01.

21.06.25, 11:35
home.cweiske.de :: dojo :: DNS server resonse times
	OKs: 2a00:f826:8:2::195 is 0.11.