novnc: correctly install and point to `websockify`

[dwf]

utils/novnc_proxy tries to download and run the websockify package in the directory where the script is located, which doesn't work because the nix store is read-only. This patches the script to point to nix-installed websockify.

As it's logically a separate change I separated this and ##188897 into separate PRs. I'll need to rebase this once #188897 is submitted.

Description of changes

Things done

• Built on platform(s)
  • [x] x86_64-linux
  • [ ] aarch64-linux
  • [ ] x86_64-darwin
  • [ ] aarch64-darwin
• [ ] For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• [ ] 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
• [x] 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/)
• 22.11 Release Notes (or backporting 22.05 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
  • [ ] (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• [x] Fits CONTRIBUTING.md.

[dwf]

@NeverBehave Any thoughts on this one?

[dwf]

@AndersonTorres Similarly, you might be an appropriate second reviewer for this PR.

[dwf]

@applePrincess Likewise, mind giving this a look?

[AndersonTorres]

As it's logically a separate change I separated this and #https://github.com/NixOS/nixpkgs/pull/188897 into separate PRs. I'll need to rebase this once https://github.com/NixOS/nixpkgs/pull/188897 is submitted.

Wait, are these changes somehow dependent?

[dwf]

Wait, are these changes somehow dependent?

They aren't, they're just so close by that I'm betting on a merge conflict. Maybe git will pleasantly surprise me.

[AndersonTorres]

Rebase

[dwf]

Done. I concatenated to the list rather than simply added an element to make it clear that the with statement is scoped/meant for to the first part, not sure if this is considered good style or not.

[AndersonTorres]

Next time you can concentrate related commits in a single PR.