docs(bruno): update API test files for media terminology

- Rename ebook_id environment variable to media_item_id
- Update scanner endpoint example paths and documentation
- Update library endpoint documentation
- Keep library type 'ebooks' where appropriate (valid type value)

bruno/library/Update Scan Settings.bru

@@ -29,7 +29,7 @@ settings {
 docs {
   ## Update Scan Settings
   
-  Updates the user's ebook scanning settings.
+  Updates the user's media scanning settings.
   
   **Method:** PUT