"Fetching OpenPGP keys" scenarios are fragile: communication failure with keyserver

The temporary solution implemented in #12211 (closed) is not robust enough: while doing #12291 (closed) I see lots of failures in August. Thankfully we’ve discussed (and agreed on) better options on #12211 (closed).

Feature Branch: bugfix/12689-more-reliable-OpenPGP-keyserver

Parent Task: #10288

Related issues

Related to #12211 (closed)
Related to #10378 (closed)
Related to #9519
Related to #15415 (closed)
Related to #17169
Blocked by #12689 (closed)
Blocks #16209

Original created by @intrigeri on 14770 (Redmine)

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