Replace ssh-askpass-sublime executable from sublime-merge that is incompatable with the nix package wrapper. Fixes #88600

Motivation for this change

Sublime merge has it's own askpass program that is used when pushing/pulling from a git repo using an ssh key with a passphrase and no ssh-agent. Currently the askpass program doesn't work (askpass dialog is never shown) due to it's custom functionality requiring it to pass a custom argv[0] argument to the sublime-merge binary which doesn't work because of the wrapper bash script added by the Nix build process to set various environment variables needed for it to run.

Things done

I've replaced the askpass program that is distributed with sublime-merge with a simple bash script that has equivalent functionality and works properly with the Nix package.

• 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.