doc: define html_context in conf.py

The dictionary html_context is not passed into conf.py but must be created
there. See
https://dev.readthedocs.io/en/latest/design/theme-context.html#customizing-the-context

Fixes: df86796028df ("doc: enable ReadTheDocs addon management")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
1 file changed