Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/test/unit/common/utils/test_utils.py

@@ -0,0 +1,34 @@
+import os
+import shutil
+import unittest
+
+from local_server.common.utils.utils import import_plugins
+from local_server.test import PROJECT_ROOT, random_string
+
+
+class TestPlugins(unittest.TestCase):
+    """ Test plugin import functionality """
+
+    plugins_dir = f"{PROJECT_ROOT}/local_server/test/plugins"
+    test_plugin_path = f"{plugins_dir}/foo.py"
+    secret = random_string(8)
+
+    @classmethod
+    def setUpClass(cls) -> None:
+        if not os.path.isdir(cls.plugins_dir):
+            os.mkdir(cls.plugins_dir)
+        with open(cls.test_plugin_path, "w") as fh:
+            fh.write(f'SECRET = "{cls.secret}"\n')
+
+    @classmethod
+    def tearDownClass(cls) -> None:
+        if os.path.isdir(cls.plugins_dir):
+            shutil.rmtree(cls.plugins_dir)
+
+    def test_import_plugins(self):
+        self.assertTrue(os.path.isfile(self.test_plugin_path))
+        loaded_modules = import_plugins("local_server.test.plugins")
+        # test that import plugins found the file
+        self.assertEqual(["local_server.test.plugins.foo"], [ele.__name__ for ele in loaded_modules])
+        # test that the module was properly executed
+        self.assertEqual(self.secret, loaded_modules[0].SECRET)