Implements GET /categories

Adds type to OpenAPI. Feature done and tested E2E.
Adds common utilities package named "golang" to overcome language
deficiencies.

Issue #27

.github/workflows/go.yml

@@ -0,0 +1,28 @@
+name: Go
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: [ '1.21', '1.22' ]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Build
+        run: go build -v ./...
+
+      - name: Test
+        run: go test -v ./...