Add mypy plugin

configurations/mypy_plugin.py

@@ -0,0 +1,15 @@
+from mypy.plugin import Options, Plugin
+
+from configurations import importer
+
+
+class DjangoConfigurationsPlugin(Plugin):
+    def __init__(self, options: Options) -> None:
+        super().__init__(options)
+        # Install settings so that they're available to other
+        # mypy plugins called after this one
+        importer.install()
+
+
+def plugin(version: str):
+    return DjangoConfigurationsPlugin