auth: add a configurable delay for notifications

[chbruyand]

Short description

Adds a configurable delay-notifications parameter to delay notifications.

Fix #12785

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 7573561075

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.0%) to 57.709%

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Totals
Change from base Build 7571071755:	1.0%
Covered Lines:	107828
Relevant Lines:	155506

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💛 - Coveralls

[Habbie]

Looks good! I wonder if pdns_control notify should be undelayed, but we can also wait and see what users think. So, approved.

[Habbie]

If you feel there is any work left, I'll wait, but otherwise, please hit Ready for review (and you might as well just merge then).

[Habbie]

If you feel there is any work left, I'll wait, but otherwise, please hit Ready for review (and you might as well just merge then).

Oh, I just realised it doesn't have docs yet!

[Habbie]

thanks, really approved now :)