Timezone feature (#8185)

* Add supported timezones into config

Remove Timezone list creation in favor of timezone from configs

Add Timezone field to Users table

Clean up format of SupportedTimezones in config

* Remove unwanted change

* Add test for updating user timezone

* Add empty map[string]string if Timezone is null

* Add EnableTimezoneSelection config

* Revert back to map[string]string for ClientConfig

* Refactor SupportedTimezones into timezones.json

* Include timezones.json in TestConfigFlag

* Add timezone api endpoint

* Bump varchar size to 256 and setMaxSize in user_store

* Refactor LoadConfig to LoadConfig and LoadTimezoneConfig

* Remove unnecessary argument in LoadConfig, mail_test

* Add test for timezone endpoint

* Add license header

* Refactor timezones endpoint to system.go

* Add system base route to timezone endpoint

* db timezone upgrade in db v4.9

* Avoid saving SupportedTimezones to config.json

* Add timezonePath support in config

* Remove EnableTimezoneSelection from config

* Use return statement without return parameter

* Refactor test for SupportedTimezones

* Check for supportedTimezone != nil instead of using len

* Decouple SupportedTimezones out of Config

* Fix failing test

* Add LastTeamIconUpdate back in upgrade.go

* Write timezone config in config_flag_test

* Add code fallback for default timezone support

model/config.go

@@ -1700,6 +1700,16 @@ func (s *MessageExportSettings) SetDefaults() {
 	}
 }
 
+type TimezoneSettings struct {
+	SupportedTimezonesPath *string
+}
+
+func (s *TimezoneSettings) SetDefaults() {
+	if s.SupportedTimezonesPath == nil {
+		s.SupportedTimezonesPath = NewString("timezones.json")
+	}
+}
+
 type ConfigFunc func() *Config
 
 type Config struct {
@@ -1733,6 +1743,7 @@ type Config struct {
 	MessageExportSettings MessageExportSettings
 	JobSettings           JobSettings
 	PluginSettings        PluginSettings
+	TimezoneSettings      TimezoneSettings
 }
 
 func (o *Config) Clone() *Config {
@@ -1802,6 +1813,7 @@ func (o *Config) SetDefaults() {
 	o.JobSettings.SetDefaults()
 	o.WebrtcSettings.SetDefaults()
 	o.MessageExportSettings.SetDefaults()
+	o.TimezoneSettings.SetDefaults()
 }
 
 func (o *Config) IsValid() *AppError {