Move coverity to a reusable workflow, add a dispatcher workflow

[rgacogne]

Short description

I need to find a way to test this, but review and comments welcome in the meantime :)

Checklist

I have:

• [x] 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 10956306354

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 17 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.02%) to 64.678%

---

Files with Coverage Reduction	New Missed Lines	%
ext/json11/json11.cpp	1	64.49%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/recursordist/syncres.cc	1	79.54%
pdns/recursordist/sortlist.cc	2	74.12%
pdns/recursordist/aggressive_nsec.cc	2	65.88%
pdns/misc.cc	2	63.26%
pdns/recursordist/test-syncres_cc2.cc	3	88.91%
pdns/opensslsigners.cc	5	61.07%
<!--	Total:	17

Totals
Change from base Build 10939216509:	0.02%
Covered Lines:	124811
Relevant Lines:	162220

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💛 - Coveralls

[rgacogne]

Wonderful, thank you for testing!