Convert the time into local timestamp of the user

Originally brought up by Tanja here: https://github.com/jakartaee/jakartaone.org/issues/352#issuecomment-978011900

The purpose of this is to show the time zone the user is in to reduce the time cluster we are having now on agenda time column (and potentially other places where we display time info)

Proposal by Martin:

We'd need to store the time zone, the timestamp, print a default, read the tz + timestamp, and replace with current tz so something like <span data-dynamic-tz="-07:00" data-dynamic-time="HH:mm">HH:mm CET</span> would be present on load then it would be converted to local using all of those values and replace the text in the span