Motivation for this change

Recently YouTube API Services team has disabled youtube-viewer API key (they reduced quota limit of queries per day for a single API key). youtube-viewer repository has been updated to allow setting your personally obtained API key.
So, for now, without updating youtube-viewer you're not able to view YouTube videos with it.

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 --pure -I nixpkgs=https://github.com/alexoundos/nixpkgs/archive/52ad14bbee1c44688acdffc6a3ac595b80adca15.tar.gz -p youtube-viewer --run "youtube-viewer"
• 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.

test the functionality in NixOS

1. Temporarily set the API key (please, do not overuse my).
   $ cp api.txt ~/.config/youtube-viewer/api.json

2. Run.

$ export NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt
$ nix-shell --pure -I nixpkgs=https://github.com/alexoundos/nixpkgs/archive/52ad14bbee1c44688acdffc6a3ac595b80adca15.tar.gz --keep NIX_SSL_CERT_FILE -p youtube-viewer --run "youtube-viewer starcraft remastered"

SSL certificate trick is mandatory for pure nix-shell and partially described in #13744 (comment).