PLT-1800 Load server side locale from the config.json (#3092)

* PLT-1800 Load server side locale from the config.json

* Add support for locales with country specifics

* Fix localization on served locale file as plain/text

utils/config.go

@@ -246,7 +246,8 @@ func getClientConfig(c *model.Config) map[string]string {
 	props["WebsocketPort"] = fmt.Sprintf("%v", *c.ServiceSettings.WebsocketPort)
 	props["WebsocketSecurePort"] = fmt.Sprintf("%v", *c.ServiceSettings.WebsocketSecurePort)
 
-	props["AllowCorsFrom"] = *c.ServiceSettings.AllowCorsFrom
+	props["DefaultClientLocale"] = *c.LocalizationSettings.DefaultClientLocale
+	props["AvailableLocales"] = *c.LocalizationSettings.AvailableLocales
 
 	if IsLicensed {
 		if *License.Features.CustomBrand {