feat: make time zone setting actually changable

pkg/routes/api/v1/user_settings.go

@@ -52,6 +52,8 @@ type UserSettings struct {
 	WeekStart int `json:"week_start"`
 	// The user's language
 	Language string `json:"language"`
+	// The user's time zone. Used to send task reminders in the time zone of the user.
+	Timezone string `json:"timezone"`
 }
 
 // GetUserAvatarProvider returns the currently set user avatar
@@ -180,6 +182,7 @@ func UpdateGeneralUserSettings(c echo.Context) error {
 	user.DefaultListID = us.DefaultListID
 	user.WeekStart = us.WeekStart
 	user.Language = us.Language
+	user.Timezone = us.Timezone
 
 	_, err = user2.UpdateUser(s, user)
 	if err != nil {

pkg/user/user.go

@@ -463,6 +463,16 @@ func UpdateUser(s *xorm.Session, user *User) (updatedUser *User, err error) {
 		}
 	}
 
+	// Check if we have a valid time zone
+	if user.Timezone == "" {
+		user.Timezone = config.GetTimeZone().String()
+	}
+
+	_, err = time.LoadLocation(user.Timezone)
+	if err != nil {
+		return
+	}
+
 	// Update it
 	_, err = s.
 		ID(user.ID).
@@ -480,6 +490,7 @@ func UpdateUser(s *xorm.Session, user *User) (updatedUser *User, err error) {
 			"default_list_id",
 			"week_start",
 			"language",
+			"timezone",
 		).
 		Update(user)
 	if err != nil {