Add list_spaces

[osanseviero]

Is your feature request related to a problem? Please describe.
Allow users listing spaces similar to how they can list models and datasets

We can use something like this for example

HF_LIST_ENDPOINT = HF_ENDPOINT + "/api/spaces?filter={type}"
r = requests.get(HF_LIST_ENDPOINT.format(type=type))
r.raise_for_status()
d = r.json()

cc @lvwerra

[LysandreJik]

Indeed, should be simple to add! I've added some labels, happy to review a PR! :)

[cakiki]

I'd like to work on this!

[osanseviero]

Sounds good! Feel free to open a PR for this and let us know if you have any questions 🔥