Add GOOGLE_ANALYTICS_TRACKING_ID environment variable to deploy workflow

- Pass repository variable GOOGLE_ANALYTICS_TRACKING_ID as environment variable during npm run build
- Configure Docusaurus to use Google Analytics when the environment variable is set

Author: chelproc

.github/workflows/deploy.yml

@@ -14,6 +14,8 @@ jobs:
         with:
           fetch-depth: 0
       - run: npm ci && npm run build
+        env:
+          GOOGLE_ANALYTICS_TRACKING_ID: ${{ vars.GOOGLE_ANALYTICS_TRACKING_ID }}
       - uses: actions/upload-pages-artifact@v3
         with:
           path: build

docusaurus.config.js

@@ -42,6 +42,9 @@ const config = {
             "./src/css/custom.css",
           ],
         },
+        gtag: process.env.GOOGLE_ANALYTICS_TRACKING_ID && {
+          trackingID: process.env.GOOGLE_ANALYTICS_TRACKING_ID,
+        },
       },
     ],
   ],