docs_deploy.yml - update to create backup and always be single release (#24781)

* docs_deploy.yml - update to create backup and always be single release

* Add build time variable to make it easier to confirm last successful deploy

docs/.vitepress/theme/index.js

@@ -37,6 +37,10 @@ export default {
     //Tabs: https://github.com/Red-Asuka/vitepress-plugin-tabs
     app.component("Tab", Tab);
     app.component("Tabs", Tabs);
+    // Global build time variable
+    app.config.globalProperties.$buildTime = JSON.stringify(
+      new Date().toISOString()
+    );
   },
 
   // to support medium zoom: https://github.com/vuejs/vitepress/issues/854

docs/en/index.md

@@ -137,3 +137,5 @@ The PX4 flight stack is hosted under the governance of the [Dronecode Project](h
 <a href="https://www.linuxfoundation.org/projects" style="padding:20px;"><img src="https://mavlink.io/assets/site/logo_linux_foundation.png" alt="Linux Foundation Logo" width="80px" /></a>
 
 <div style="padding:10px">&nbsp;</div>
+
+Doc build time: {{ $buildTime }}