Flask App factory PR #1 (#8418)

* First cut at app factory

* Setting things back to master

* Working with new FLASK_APP

* Still need to refactor Celery

* CLI mostly working

* Working on unit tests

* Moving cli stuff around a bit

* Removing get in config

* Defaulting test config

* Adding flask-testing

* flask-testing casing

* resultsbackend property bug

* Fixing up cli

* Quick fix for KV api

* Working on save slice

* Fixed core_tests

* Fixed utils_tests

* Most tests working - still need to dig into remaining app_context issue in tests

* All tests passing locally - need to update code comments

* Fixing dashboard tests again

* Blacking

* Sorting imports

* linting

* removing envvar mangling

* blacking

* Fixing unit tests

* isorting

* licensing

* fixing mysql tests

* fixing cypress?

* fixing .flaskenv

* fixing test app_ctx

* fixing cypress

* moving manifest processor around

* moving results backend manager around

* Cleaning up __init__ a bit more

* Addressing PR comments

* Addressing PR comments

* Blacking

* Fixes for running celery worker

* Tuning isort

* Blacking

superset/utils/feature_flag_manager.py

@@ -0,0 +1,39 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from copy import deepcopy
+
+
+class FeatureFlagManager:
+    def __init__(self) -> None:
+        super().__init__()
+        self._get_feature_flags_func = None
+        self._feature_flags = None
+
+    def init_app(self, app):
+        self._get_feature_flags_func = app.config.get("GET_FEATURE_FLAGS_FUNC")
+        self._feature_flags = app.config.get("DEFAULT_FEATURE_FLAGS") or {}
+        self._feature_flags.update(app.config.get("FEATURE_FLAGS") or {})
+
+    def get_feature_flags(self):
+        if self._get_feature_flags_func:
+            return self._get_feature_flags_func(deepcopy(self._feature_flags))
+
+        return self._feature_flags
+
+    def is_feature_enabled(self, feature):
+        """Utility function for checking whether a feature is turned on"""
+        return self.get_feature_flags().get(feature)