[Backport release-24.05] grafana-agent: 0.40.5 -> 0.42.0

[emilylange]

Description of changes

Backport of:

• grafana-agent: 0.40.5 -> 0.41.0 #316736
• grafana-agent: 0.41.0 -> 0.41.1 #318063
• grafana-agent: 0.41.1 -> 0.42.0 #331906

All cherry-picks applied cleanly. Meaning the GitHub backport action would have worked, but also would have opened 3 PR instead of 1.

Note that both https://github.com/grafana/agent/releases/tag/v0.41.0 and https://github.com/grafana/agent/releases/tag/v0.41.1 had minor breaking changes.

• @tamara-schmitz requested the bump to 0.42.0 (grafana-agent: 0.41.1 -> 0.42.0 #331906) to be backported due to the various security fixes in grafana-agent: 0.41.1 -> 0.42.0 #331906 (comment).
• @katexochen added the backport label to the bump to 0.41.1 (grafana-agent: 0.41.0 -> 0.41.1 #318063).

Given how minor the breaking changes are in combination with the multiple requests to backport the many included security fixes, backporting should be fine.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.