Expose user-facing classes on session level

Shorten previous nested imports

Author: FlorentinD

graphdatascience/gds_session/__init__.py

@@ -0,0 +1,13 @@
+from .gds_sessions import GdsSessions, SessionInfo, AuraAPICredentials
+from .dbms_connection_info import DbmsConnectionInfo
+from .session_sizes import SessionSizes
+
+__all__ = [
+    GdsSessions,
+    SessionInfo,
+    DbmsConnectionInfo,
+    AuraAPICredentials,
+    SessionSizes,
+]
+
+