feat(frontend): dark and high contrast theme supported EE-909 (#5353)

* feat dark theme & high contrast theme supported

api/http/handler/users/user_update.go

@@ -17,6 +17,7 @@ import (
 type userUpdatePayload struct {
 	Username string `validate:"required" example:"bob"`
 	Password string `validate:"required" example:"cg9Wgky3"`
+	UserTheme string `example:"dark"`
 	// User role (1 for administrator account and 2 for regular account)
 	Role int `validate:"required" enums:"1,2" example:"2"`
 }
@@ -104,6 +105,10 @@ func (handler *Handler) userUpdate(w http.ResponseWriter, r *http.Request) *http
 		user.Role = portainer.UserRole(payload.Role)
 	}
 
+	if payload.UserTheme != "" {
+		user.UserTheme = payload.UserTheme
+	}
+
 	err = handler.DataStore.User().UpdateUser(user.ID, user)
 	if err != nil {
 		return &httperror.HandlerError{http.StatusInternalServerError, "Unable to persist user changes inside the database", err}