lint: Add linters to makefile / github CI

Not yet ready to make gating, but we can watch the progress.

.github/workflows/main.yml

@@ -46,3 +46,30 @@ jobs:
         working-directory: git-sync
         run: |
           make test
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up go
+        uses: actions/setup-go@v4
+        with:
+          go-version: '1.20.6'
+
+      - uses: actions/checkout@v3
+        with:
+          path: git-sync
+
+      # We run the github action, even though this is duplicated in `make lint` below.
+      # This is because the action gives easier-to-read output than the linter.
+      # There is a risk of drift between the two, but this is only linting,
+      # not runtime correctness!
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v3
+        with:
+          working-directory: git-sync
+          version: v1.53.3
+
+      - name: make lint
+        working-directory: git-sync
+        run: |
+          make lint

Makefile

@@ -276,3 +276,11 @@ container-clean:
 
 bin-clean:
 	rm -rf .go bin
+
+lint-staticcheck:
+	go run honnef.co/go/tools/cmd/staticcheck@2023.1.3
+
+lint-golangci-lint:
+	go run github.com/golangci/golangci-lint/cmd/golangci-lint@v1.53.3 run
+
+lint: lint-staticcheck lint-golangci-lint