Fix missing timezone errors

Done

Some countries are missing timezone values, but they have country aliases that has the same timezone values
Check if country has missing timezone and get the timezone from their respective aliases
Added fallback country (GB) for invalid timezone queries

Check out https://ubuntu-com-14000.demos.haus/
For valid timezones, check that the country code and country shown is as expected. Query:
- /user-country-tz.json?tz=Asia/Kuala_Lumpur
- /user-country-tz.json?tz=America/Mendoza
For invalid timezones, the fallback value should be { "country": "United Kingdom", "country_code": "GB" }. Query:
- /user-country-tz.json?tz=Etc/GMT-8
- /user-country-tz.json?tz=test

[If relevant, please include a screenshot.]