pam-moduler: Add first implementation of a Go PAM Module generator

A PAM module can be generated using pam-moduler and implemented fully in
go without having to manually deal with the C setup.

Module can be compiled using go generate, so go:generate directives can be
used to make this process automatic, with a single go generate call as shown
in the example.

.github/workflows/test.yaml

@@ -18,6 +18,12 @@ jobs:
       run: sudo useradd -d /tmp/test -p '$1$Qd8H95T5$RYSZQeoFbEB.gS19zS99A0' -s /bin/false test
     - name: Checkout code
       uses: actions/checkout@v4
+    - name: Generate example module
+      run: |
+        rm -f example-module/pam_go.so
+        go generate -C example-module -v
+        test -e example-module/pam_go.so
+        git diff --exit-code example-module
     - name: Test
       run: sudo go test -v -cover -coverprofile=coverage.out ./...
     - name: Upload coverage reports to Codecov