Make load_profile importable from aiida module

load_profile() is widely used and documented. Exposing it as API under
aiida module directly can make a bunch of LSP happy.

src/aiida/__init__.py

@@ -35,6 +35,7 @@
 )
 __paper_short__ = 'S. P. Huber et al., Scientific Data 7, 300 (2020).'
 
+__all__ = ['load_profile']
 
 def get_strict_version():
     """Return a distutils StrictVersion instance with the current distribution version