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

utils/config_test.go

@@ -21,6 +21,15 @@ func TestConfig(t *testing.T) {
 	InitTranslations(cfg.LocalizationSettings)
 }
 
+func TestTimezoneConfig(t *testing.T) {
+	TranslationsPreInit()
+	supportedTimezones := LoadTimezones("timezones.json")
+	assert.Equal(t, len(supportedTimezones) > 0, true)
+
+	supportedTimezones2 := LoadTimezones("timezones_file_does_not_exists.json")
+	assert.Equal(t, len(supportedTimezones2) > 0, true)
+}
+
 func TestFindConfigFile(t *testing.T) {
 	dir, err := ioutil.TempDir("", "")
 	require.NoError(t, err)

utils/timezone.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package utils
+
+import (
+	"encoding/json"
+	"io/ioutil"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func LoadTimezones(fileName string) model.SupportedTimezones {
+	var supportedTimezones model.SupportedTimezones
+
+	if timezoneFile := FindConfigFile(fileName); timezoneFile == "" {
+		return model.DefaultSupportedTimezones
+	} else if raw, err := ioutil.ReadFile(timezoneFile); err != nil {
+		return model.DefaultSupportedTimezones
+	} else if err := json.Unmarshal(raw, &supportedTimezones); err != nil {
+		return model.DefaultSupportedTimezones
+	} else {
+		return supportedTimezones
+	}
+}