Ability to add timezone field/data to contact

Is your feature request related to a problem? Please describe.

For AntennaPod I regularly need to schedule meetings with some of our contributors who are all over the world. We don't meet that regularly, but each time I need to consider their timezones (without knowing their addresses). In some cases I remember, in most cases I have to ask again. I'd love, therefore, to be able to record this info in my contacts.

Describe the solution you'd like

When editing a contact, then clicking on "Add more info" and "More fields", show the option "Time zone". The field, when visible, ideally is a 'smart drop-down', similar to spoken languages. Don't know if it should be possible to add multiple time zones to a single contact or not.

Describe alternatives you've considered

Infer the timezone from the address, but I don't need or want their detailed address, so I'd rather manually enter this information.

Additional context

It seems TZ is already supported (#1264) but I don't see it in the interface (I'm on NC 27.1.3). Also related: #3214.

Start with the contact editor's “Add more info” and “More fields” entry points, then review issues #1264 and #3214 for the existing timezone support and related context. Done means a contact can expose and edit a timezone through the interface, with the single- versus multiple-timezone behavior resolved.