Add timezone to public calendar

[itrich]

As @wwentland correctly noted, the public calendar on scs.community/contribute should make clear that all events are noted in CET.

Maybe we can add a switch to other timezones?

[wwentland]

Thank you! I would also like to point out that the events shown on https://scs.community/contribute/ are displayed in CET, while the "red bar" that denotes the current time references the local time.

Taken together, all three aspects result in the impression that meetings are taking place at a different (and incorrect) time for all users that reside outwith the CET timezone.

[itrich]

This was partially fixed by SovereignCloudStack/website#508

We should however add a button to switch between CET/GMT+1 and local time view.

[itrich]

Transfered to docs-page as we'll maintain the calendar here for the future.