[ical] Add user-agent to prevent request error on some sites
[ical] Add user-agent to prevent request error on some sites

When fetching URL from airbnb, server return a 401 if request has no
User-agent

clochix/konnectors,poupotte/konnectors,poupotte/konnectors,clochix/konnectors,cozy-labs/konnectors,clochix/konnectors,cozy-labs/konnectors,poupotte/konnectors,cozy-labs/konnectors