update docs to remove /alpha

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

docs/plugins/integrating-search-into-plugins.md

@@ -227,7 +227,7 @@ import { createBackend } from '@backstage/backend-defaults';
 //...
 const backend = createBackend();
 // Installing the search backend plugin
-backend.add(import('@backstage/plugin-search-backend/alpha'));
+backend.add(import('@backstage/plugin-search-backend'));
 // Installing the newly created faq snippets collator module
 backend.add(
   import(

docs/plugins/proxying.md

@@ -20,7 +20,7 @@ The plugin is already added to a default Backstage project.
 To add it to a project, add the following line in `packages/backend/src/index.ts`:
 
 ```ts
-backend.add(import('@backstage/plugin-proxy-backend/alpha'));
+backend.add(import('@backstage/plugin-proxy-backend'));
 ```
 
 ### Old Backend
@@ -28,7 +28,7 @@ backend.add(import('@backstage/plugin-proxy-backend/alpha'));
 In `packages/backend/src/index.ts`:
 
 ```ts
-backend.add(import('@backstage/plugin-proxy-backend/alpha'));
+backend.add(import('@backstage/plugin-proxy-backend'));
 ```
 
 ## Configuration