[External APIs] Automatic timezones

[eclipse-909]

Description

When the user creates or updates user-created events, it would be convenient if the timezone was automatically set based on the location of that event. This will require a 3rd party API call to get the IANA canonical timezone identifier from the provided location (street address, city, country, and postal code).

Acceptance Criteria

• When creating or updating an event's hard start/end...
  If the location is provided and is a real location that exists, the timezone for that location is forced for the hard start/end.
  To get timezone from a location, look to see if the browser has something built in that can do this. If not, look for some public/free API that does this. If not, we can use google maps when we get that going.

Developer Notes

• Google Maps should have something like this, but we should first see if there are any free/public APIs that can do this.
• frontend/src/models/itinerary.rs has a table of IANA canonical timezone identifiers called TIMEZONES. This list may need to be adjusted depending on what data the 3rd party API gives us.