Disable Google Analytics on preview builds

Preview builds were firing page view events into the production GA
property, inflating metrics with internal review traffic. Skip the
@docusaurus/plugin-google-gtag plugin when DOCUSAURUS_IS_PREVIEW=true
is set by pr-preview.yml.

Author: AdamGohs

.github/workflows/pr-preview.yml

@@ -36,6 +36,7 @@ jobs:
         env:
           DOCUSAURUS_URL: https://usace-rmc.github.io
           DOCUSAURUS_BASE_URL: /RMC-Software-Documentation-Previews/pr-${{ github.event.pull_request.number }}/
+          DOCUSAURUS_IS_PREVIEW: 'true'
         run: npm run build
       - uses: peaceiris/actions-gh-pages@v4
         with:

docusaurus.config.js

@@ -89,14 +89,20 @@ export default {
   ],
 
   plugins: [
-    // Google Analytics plugin
-    [
-      '@docusaurus/plugin-google-gtag',
-      {
-        trackingID: 'G-LB2BWWGDTB',
-        anonymizeIP: true,
-      },
-    ],
+    // Google Analytics plugin — production builds only.
+    // Preview builds set DOCUSAURUS_IS_PREVIEW=true so they don't pollute
+    // the production GA property with pr-preview page views.
+    ...(process.env.DOCUSAURUS_IS_PREVIEW === 'true'
+      ? []
+      : [
+          [
+            '@docusaurus/plugin-google-gtag',
+            {
+              trackingID: 'G-LB2BWWGDTB',
+              anonymizeIP: true,
+            },
+          ],
+        ]),
 
     // TailwindCSS as a custom plugin
     tailwindPlugin,