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

api4/system.go

@@ -17,6 +17,8 @@ import (
 func (api *API) InitSystem() {
 	api.BaseRoutes.System.Handle("/ping", api.ApiHandler(getSystemPing)).Methods("GET")
 
+	api.BaseRoutes.System.Handle("/timezones", api.ApiSessionRequired(getSupportedTimezones)).Methods("GET")
+
 	api.BaseRoutes.ApiRoot.Handle("/config", api.ApiSessionRequired(getConfig)).Methods("GET")
 	api.BaseRoutes.ApiRoot.Handle("/config", api.ApiSessionRequired(updateConfig)).Methods("PUT")
 	api.BaseRoutes.ApiRoot.Handle("/config/reload", api.ApiSessionRequired(configReload)).Methods("POST")
@@ -378,6 +380,18 @@ func getAnalytics(c *Context, w http.ResponseWriter, r *http.Request) {
 	w.Write([]byte(rows.ToJson()))
 }
 
+func getSupportedTimezones(c *Context, w http.ResponseWriter, r *http.Request) {
+	supportedTimezones := c.App.Timezones()
+
+	if supportedTimezones != nil {
+		w.Write([]byte(model.TimezonesToJson(supportedTimezones)))
+		return
+	}
+
+	emptyTimezones := make([]string, 0)
+	w.Write([]byte(model.TimezonesToJson(emptyTimezones)))
+}
+
 func testS3(c *Context, w http.ResponseWriter, r *http.Request) {
 	cfg := model.ConfigFromJson(r.Body)
 	if cfg == nil {