[IMP] conf: remove pillow inventory, cache werkzeug

The pallets website is regularly unreachable (due to DNS failures so it's not even that we get rate limited even though we probably hit it excessively), which causes a warning during documentation build, which in turn causes a completely unnecessary build failure.

Some werkzeug links seem to be generated (in the backend docs), so just commit the werkzeug inventory file as it's pretty small.

Also remove the pillow inventory entirely, it doesn't seem to cause issues but also seems completely unused.

closes odoo/documentation#13698

Forward-port-of: odoo/documentation#13669
Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>

conf.py

@@ -212,9 +212,9 @@ extensions.append('sphinx.ext.graphviz' if shutil.which('dot') else 'graphviz_pl
 todo_include_todos = False
 
 intersphinx_mapping = {
-    'pillow': ('https://pillow.readthedocs.io/en/stable/', None),
     'python': ('https://docs.python.org/3/', None),
-    'werkzeug': ('https://werkzeug.palletsprojects.com/en/2.3.x/', None),
+    # apparently local inventories are relative to the source dir?
+    'werkzeug': ('https://werkzeug.palletsprojects.com/', '../invs/werkzeug.inv'),
 }
 
 github_user = 'odoo'