feat(v2): docs version configuration: lastVersion, version.{path,label} (#3357)

* add new docs versioning options

* Add some tests for new versioning options

* Add some docs for version configurations

* try to fix broken link detection after /docs/ root paths have been removed on deploy previews

* improve dev/deploypreview versioning configurations

* disable custom current version path, as it produces broken links

* readVersionDocs should not be order sensitive

* fix versions page according to versioning config

* fix versions page according to versioning config

website/docs/using-plugins.md

@@ -335,6 +335,33 @@ module.exports = {
          * in `/docs/next` directory, only versioned docs.
          */
         excludeNextVersionDocs: false,
+        /**
+         * The last version is the one we navigate to in priority on versioned sites
+         * It is the one displayed by default in docs navbar items
+         * By default, the last version is the first one to appear in versions.json
+         * By default, the last version is at the "root" (docs have path=/docs/myDoc)
+         * Note: it is possible to configure the path and label of the last version
+         * Tip: using lastVersion: 'current' make sense in many cases
+         */
+        lastVersion: undefined,
+        /**
+         * The docusaurus versioning defaults don't make sense for all projects
+         * This gives the ability customize the label and path of each version
+         * You may not like that default versin
+         */
+        versions: {
+          /*
+          Example configuration: 
+          current: {
+            label: 'Android SDK v2.0.0 (WIP)',
+            path: 'android-2.0.0',
+          },
+          '1.0.0': {
+            label: 'Android SDK v1.0.0',
+            path: 'android-1.0.0',
+          },
+          */
+        },
       },
     ],
   ],