Motivation for this change

The programs.chromium.extensions option currently appends the chrome web store update URL to the extension ID for the ExtensionInstallForcelist option. As indicated by the documentation for ExtensionInstallForcelist this is not necessary as it is already the default.

Removing this implicit default would allow a user to more easily install extensions not in the chrome web store by setting the update URL themselves. An example was also added to the documentation.

If an alternative schema for this option is desired, I am open to it. Maybe a list of { id= "..."; updateURL = "..."; } attrsets? I tried to just do a minimal change that wouldn't break any existing configs.

Also relevant to this PR is #76863 which would be nicer but probably requires a lot more work.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.