feat: Auto-populate the telephone code based on the browser timezone (#10146)

Fixes https://github.com/chatwoot/chatwoot/issues/6228


There is a country code selector for the phone input field. This is
often a point of frustration. See the response below.

> We are using the phone number field however this can be frustrating
for customers, especially mobile users, to select the +1 US country
code. Our users are typically local businesses and being able to default
to +1 country code in the phone number field or the account would
improve the interaction they have with customers.


Most people who run local businesses don't need a country selector.
However, to preserve the quality of the data we store, we need a country
code.

A balance between these two issues can be found with an auto-populating
country code field based on the browser's timezone. This is what I did
in this PR. Based on the browser timezone, we will resolve it to the
closest country code.

app/javascript/shared/components/PhoneInput/helper.js

@@ -0,0 +1,13 @@
+import { getPhoneCodeByTimezone } from 'timezone-phone-codes';
+import ct from 'countries-and-timezones';
+
+const getTimezone = () => Intl.DateTimeFormat().resolvedOptions().timeZone;
+
+export const getActiveDialCode = () => {
+  return getPhoneCodeByTimezone(getTimezone()) || '';
+};
+
+export const getActiveCountryCode = () => {
+  const country = ct.getCountryForTimezone(getTimezone()) || {};
+  return country.id || '';
+};