Automatically update the controller version (#57)

Create a new GitHub Actions workflow to submit a pull request for new controller versions.

.github/workflows/ci.yaml

@@ -42,9 +42,9 @@ jobs:
       - uses: "actions/setup-go@v2"
         with:
           go-version: "${{ env.GO_VERSION }}"
-      - run: "go get golang.org/x/tools/cmd/stringer"
+      - run: "go install golang.org/x/tools/cmd/stringer"
 
-      - run: "go generate ./..."
+      - run: "go generate unifi/device.go"
       - run: "git diff --compact-summary --exit-code"
 
   lint: