gopass: Support passAlias parameter in derivation

Add a `passAlias` to `gopass` derivation, similarly to how there's `viAlias` parameter supported by vim/neovim derivations.
Apart from convenience this is also necessary for e.g. making `docker-credential-helpers` work without patching the latter - the package uses `pass` executable from `PATH` f78081d1f7/pass/pass_linux.go (L67). By setting `passAlias` to `true` (e.g. via overlays like so: 94971f34db/nixpkgs/overlays.nix (L315-L317)), secure Docker authentication via `gopass` "just works"™

pkgs/tools/security/gopass/default.nix

@@ -1,4 +1,11 @@
-{ stdenv, buildGoModule, fetchFromGitHub, git, gnupg, xclip, wl-clipboard, installShellFiles, makeWrapper }:
+{ stdenv, makeWrapper
+, buildGoModule, fetchFromGitHub, installShellFiles
+, git
+, gnupg
+, xclip
+, wl-clipboard
+, passAlias ? false
+}:
 
 buildGoModule rec {
   pname = "gopass";
@@ -28,6 +35,8 @@ buildGoModule rec {
       $out/bin/gopass completion $shell > gopass.$shell
       installShellCompletion gopass.$shell
     done
+  '' + stdenv.lib.optionalString passAlias ''
+    ln -s $bin/bin/gopass $bin/bin/pass
   '';
 
   postFixup = ''