Updated the API docs for homepage shelves endpoint (#17054)
Updated the API docs for homepage shelves endpoint (#17054)

The API response was incorrect for the /shelves/ endpoint. It mentions
headline instead of title and cta.text instead of footer.text. The
documentation needs to be updated to reflect the actual API response.
mozilla/addons-server,bqbn/addons-server,wagnerand/addons-server,mozilla/olympia,bqbn/addons-server,wagnerand/addons-server,bqbn/addons-server,mozilla/olympia,diox/olympia,mozilla/olympia,mozilla/olympia,mozilla/addons-server,mozilla/addons-server,wagnerand/addons-server,diox/olympia,mozilla/addons-server,wagnerand/addons-server,diox/olympia,diox/olympia,bqbn/addons-server