Feature/improves multiple databases support (#561)

* feat: adds docker local files to ignore

* feat: adds replica key to django q settings

* feat: adds multiple database routers testing utility

* feat: ensures scheduler works with multiple databases and replicas

* feat: adds docker image to support containerized development

* refactor: removes unnecessary import

* style: improves import styling

* docs: adds replica setting to configure documentation

django_q/tests/testing_utilities/multiple_database_routers.py

@@ -0,0 +1,38 @@
+class TestingReplicaDatabaseRouter:
+    """
+    A router to control all database operations on models in the
+    auth application.
+    """
+
+    def db_for_read(self, model, **hints):
+        """
+        Allows read access from REPLICA database.
+        """
+        return "replica"
+
+    def db_for_write(self, model, **hints):
+        """
+        Always write to DEFAULT database
+        """
+        return "default"
+
+
+class TestingMultipleAppsDatabaseRouter:
+    """
+    A router to control all database operations on models in the
+    auth application.
+    """
+
+    @staticmethod
+    def is_admin(model):
+        return model._meta.app_label in ['admin']
+
+    def db_for_read(self, model, **hints):
+        if self.is_admin(model):
+            return 'admin'
+        return 'default'
+
+    def db_for_write(self, model, **hints):
+        if self.is_admin(model):
+            return 'admin'
+        return 'default'