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/cache_manager.py

@@ -0,0 +1,56 @@
+# 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 typing import Optional
+
+from flask import Flask
+from flask_caching import Cache
+
+
+class CacheManager:
+    def __init__(self) -> None:
+        super().__init__()
+
+        self._tables_cache = None
+        self._cache = None
+
+    def init_app(self, app):
+        self._cache = self._setup_cache(app, app.config.get("CACHE_CONFIG"))
+        self._tables_cache = self._setup_cache(
+            app, app.config.get("TABLE_NAMES_CACHE_CONFIG")
+        )
+
+    @staticmethod
+    def _setup_cache(app: Flask, cache_config) -> Optional[Cache]:
+        """Setup the flask-cache on a flask app"""
+        if cache_config:
+            if isinstance(cache_config, dict):
+                if cache_config.get("CACHE_TYPE") != "null":
+                    return Cache(app, config=cache_config)
+            else:
+                # Accepts a custom cache initialization function,
+                # returning an object compatible with Flask-Caching API
+                return cache_config(app)
+
+        return None
+
+    @property
+    def tables_cache(self):
+        return self._tables_cache
+
+    @property
+    def cache(self):
+        return self._cache