Temporary exclude the common.sql.core.py from sphinx-apidoc target

With the new release of SQLAlchemy(1.4.27) TypeDecorator used
in common/sql/core.py file started failing (below error). I am not sure
if it is valid issue in SQLAlchemy or in our code base and we need to
blacklist the SQLAlchemy 1.4.27 version in requirements. But to unblock
the gate let's exclude it from sphinx-apidoc target.

Error:

Warning, treated as error:
/opt/stack/keystone/keystone/common/sql/core.py:docstring of keystone.common.sql.core.DateTimeInt.process_bind_param:19:undefined label: types_typedecorator

-https: //zuul.opendev.org/t/openstack/build/b2ee464fa1554cb89dc8873486865151
Change-Id: I7de055c2b266430bf886e200c3d8829a48ae9600

doc/source/conf.py

@@ -55,7 +55,11 @@ apidoc_output_dir = 'api'
 apidoc_excluded_paths = [
     'tests/*',
     'tests',
-    'test']
+    'test',
+    # TODO(gmann): with new release of SQLAlchemy(1.4.27) TypeDecorator used
+    # in common/sql/core.py file started failing. Remove this oncethe issue of
+    # TypeDecorator is fixed.
+    'common/sql/core.py']
 apidoc_separate_modules = True
 
 # sphinxcontrib.seqdiag options