Export calendar as ICS (webcal)

[XeR]

It would be nice to have an endpoint that exports the CTF list as ICS
Ideally, we would like to have a link with a unique token (/ctf.ics?key=4314c35c-9d38-40ef-aa18-8e1093fabbfc) otherwise it'll leak the CTF list to outsiders

[B-i-t-K]

Feature added with #116