Remove unnecessary scopes from temp key, add settings-key docs

docs/references/migrations/migration-appwrite-settings-key.md

@@ -0,0 +1 @@
+Generate a short-lived console-scoped API key for settings migration. This key allows the migration source to access project platforms and keys on the source instance.

src/Appwrite/Platform/Workers/Migrations.php

@@ -317,8 +317,6 @@ class Migrations extends Action
                 'functions.write',
                 'tokens.read',
                 'tokens.write',
-                'platforms.read',
-                'keys.read',
             ]
         ]);