Make print-build-logs a setting

[edolstra]

Motivation

This allows you to put print-build-logs = true in nix.conf. It also implicitly adds --no-print-build-logs.

Context

Issue #5858.

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• documentation in the internal API docs
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

Priorities

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[edolstra]

Adding a log-format setting is slightly trickier, since the old and new CLI have different defaults.

[cole-h]

As someone who tried to get something very similar in before (but much more wide-reaching: #3961), I'd be very very happy to see this merged!

[Ericson2314]

Adding a log-format setting is slightly trickier, since the old and new CLI have different defaults.
Can't we just agument a enum with an extra case "default", which keeps the current per-CLI defaults?

I would rather have that than the print-build-logs setting.

[Ericson2314]

Yeah just make it std::optional<LogFormat>

[edolstra]

Yeah just make it std::optional<LogFormat>

It's not that easy, because setting log-format in nix.conf would change the behaviour of both the old and new CLI, which is probably not what you want. E.g. setting log-format = bar-with-logs to enable log output would change the old CLI to use the progress bar.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-06-02-nix-team-meeting-minutes-59/28666/1

[Qyriad]

This PR needs a rebase, but is there anything else blocking it?