sphinx: add todo extention, to typeset TODO notes

also enable displaying TODO by defaults, as this is devel-oriented doc

swh/docs/sphinx/conf.py

@@ -30,6 +30,7 @@ extensions = [
     "sphinx.ext.graphviz",
     "sphinx_click.ext",
     "myst_parser",
+    "sphinx.ext.todo",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -136,6 +137,9 @@ autodoc_mock_imports = ["rados"]
 
 modindex_common_prefix = ["swh."]
 
+# For the todo extension. Todo and todolist produce output only if this is True
+todo_include_todos = True
+
 # for the extlinks extension, sub-projects should fill that dict
 extlinks: Dict = {}