feat(functions): Rename KIT_INSTANCE_ID env var to FIREBASE_KIT_INSTANCE_ID

Renamed the KIT_INSTANCE_ID environment variable to FIREBASE_KIT_INSTANCE_ID in both functions.py and tests.

Author: inlined

firebase_admin/functions.py

@@ -248,7 +248,7 @@ def _resolve_resource(self, scope: FunctionScope) -> Tuple[Resource, Optional[st
         extension_or_kit_id = None
 
         if scope.type == 'current':
-            kit_instance_id = os.environ.get('KIT_INSTANCE_ID')
+            kit_instance_id = os.environ.get('FIREBASE_KIT_INSTANCE_ID')
             if kit_instance_id:
                 resource_id = f'kit-{kit_instance_id}-{resource_id}'
                 extension_or_kit_id = kit_instance_id

tests/test_functions.py

@@ -303,7 +303,7 @@ def test_enqueue_current_scope_env_vars_ext(self, monkeypatch):
         assert recorder[0].url == expected_url
 
     def test_enqueue_current_scope_env_vars_kit(self, monkeypatch):
-        monkeypatch.setenv('KIT_INSTANCE_ID', 'my-kit')
+        monkeypatch.setenv('FIREBASE_KIT_INSTANCE_ID', 'my-kit')
         expected_queue = 'kit-my-kit-test-function-name'
         response_payload = json.dumps({
             'name': (