App/Backend should import techdocs plugin only, not common package

If a backstage App wants to enable techdocs plugin, it should only have to care about installing @backstage/plugin-techdocs and @backstage/plugin-techdocs-backend.
@backstage/plugin-techdocs-backend should re-export necessary APIs from techdocs-common

packages/create-app/templates/default-app/packages/backend/src/plugins/techdocs.ts

@@ -1,11 +1,11 @@
 import {
   createRouter,
   DirectoryPreparer,
-  CommonGitPreparer,
   Preparers,
   Generators,
-  Publisher,
   TechdocsGenerator,
+  CommonGitPreparer,
+  Publisher,
 } from '@backstage/plugin-techdocs-backend';
 import { PluginEnvironment } from '../types';
 import Docker from 'dockerode';