Add Python standard library to Intersphinx mapping (#10523)

This is good for the resolution of just over 200 failed Sphinx
references, almost all of which are from Sphinx attempting to insert
links in type hints.  Those aren't super important, but it's nice in the
vein of being able to use Sphinx's `nitpicky` mode to find places where
we have Sphinx references that are failing to resolve, since it silences
some of the noise.

(cherry picked from commit b3b59e9)

docs/conf.py

@@ -76,6 +76,7 @@
     "qiskit-aer": ("https://qiskit.org/ecosystem/aer/", None),
     "numpy": ("https://numpy.org/doc/stable/", None),
     "matplotlib": ("https://matplotlib.org/stable/", None),
+    "python": ("https://docs.python.org/3/", None),
 }
 
 # ----------------------------------------------------------------------------------