Rename to performance

This is consistent with the old performance platform URLs, which were
gov.uk/performance, and others that we have like /pricing and /features

app/main/__init__.py

@@ -27,7 +27,7 @@ from app.main.views import (  # noqa isort:skip
     new_password,
     notifications,
     organisations,
-    performance_platform,
+    performance,
     platform_admin,
     providers,
     register,