GH actions: check that only pinned pip packages are pulled when building docs

[romeroalx]

Short description

Checks that only pinned pip packages are pulled when building docs in GH actions. Attempts to solve #13046.

Uses a pip-cache mirror image for logging the actual packages pulled from an external pip repository

Adds pip pinning for recursor and dnsdist docs and updates the list for auth docs.

Checklist

I have:

• [x] read the CONTRIBUTING.md document
• [ ] compiled this code
• [x] tested this code
• [ ] included documentation (including possible behaviour changes)
• [ ] documented the code
• [ ] added or modified regression test(s)
• [ ] added or modified unit test(s)
• [ ] checked that this code was merged to master

[coveralls]

Pull Request Test Coverage Report for Build 8784833260

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 23 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.01%) to 59.513%

---

Files with Coverage Reduction	New Missed Lines	%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/opensslsigners.cc	2	60.93%
modules/lmdbbackend/lmdbbackend.cc	2	73.61%
pdns/misc.cc	2	61.76%
pdns/misc.hh	3	82.66%
pdns/packethandler.cc	3	73.0%
pdns/signingpipe.cc	10	83.87%
<!--	Total:	23

Totals
Change from base Build 8783289845:	0.01%
Covered Lines:	114110
Relevant Lines:	159289

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💛 - Coveralls