ci: add simple GitHub actions vectorlint CI

Ensures the Go code remains nicely formatted, that `go mod tidy` has
been run, that the code builds without error, and that the `vectorlint`
tool finds no issues.

Author: cpu

.github/workflows/vectorlint.yml

@@ -0,0 +1,38 @@
+name: Vector Lint
+
+permissions:
+  contents: read
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    name: Lint vectors/schemas
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Check if modules are tidy
+        run: |
+          go mod tidy
+          if [ -n "$(git status --porcelain go.mod go.sum)" ]; then
+            echo "go.mod or go.sum are not tidy. Please run 'go mod tidy' locally and commit changes."
+            git diff go.mod go.sum
+            exit 1
+          fi
+
+      - name: Verify formatting
+        # 'gofmt -l .' to list files whose formatting differs from gofmt's
+        # 'test -z' to verify that the output is empty
+        run: test -z "$(gofmt -l .)"
+
+      - name: Run vectorlint
+        run: go run ./tools/vectorlint