docs: enable httpdomain sphinx extension

note: this was enabled only for swh-web, but it really needs to also be in
swh-docs, because we pull there docs from individual modules

swh/docs/sphinx/conf.py

@@ -14,7 +14,8 @@ author = 'the Software Heritage developers'
 # ones.
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.napoleon',
-              'sphinx.ext.intersphinx']
+              'sphinx.ext.intersphinx',
+              'sphinxcontrib.httpdomain']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']