sotp: Add 1.0.0-unstable-2024-05-20

Version 1.0.0 doesn't build because of a dependency problem.

```
missing go.sum entry for module providing package
google.golang.org/appengine/urlfetch (imported by golang.org/x/oauth2/internal)
```

The upstream repository has an open PR to license the project under
MPL-2.0 but it's on hold because they might opt for Apache-2.0 instead.
The project is clearly intended to be licensed under an open license but
until getsops/sotp#1 is resolved it is to be considered unfree software.

default.nix

@@ -17,4 +17,6 @@
   apps = {
     firefox = pkgs.callPackage ./pkgs/darwin/apps/firefox {};
   };
+
+  sotp = pkgs.callPackage ./pkgs/sotp {};
 }

pkgs/sotp/default.nix

@@ -0,0 +1,26 @@
+{ buildGoModule, fetchFromGitHub, lib }:
+
+buildGoModule rec {
+  pname = "sotp";
+  version = "1.0.0-unstable-2024-05-20";
+
+  src = fetchFromGitHub {
+    owner = "getsops";
+    repo = "sotp";
+    rev = "13b0f90378a9f805806a2f5a87c4ed4afb8e877e";
+    hash = "sha256-OuUnjT0yZrZtpfhMCMqaPZMDTVBynTWTLnGaCsdWeu4=";
+  };
+
+  vendorHash = "sha256-78dS9GPuQ7HdDufql8QYxbRm6sgajd5kGiaKW6x7lTI=";
+
+  # Tests require a PGP key that is not public.
+  doCheck = false;
+
+  meta = with lib; {
+    description = "Small utility to store AWS TOTP secrets into Sops encrypted"
+                + "files and generate OTP on the command line";
+    homepage = "https://github.com/getsops/sotp";
+    license = with licenses; unfree;
+    maintainers = with maintainers; [ toonn ];
+  };
+}