feat(api): introduce new datastore interface (#3802)

* feat(api): introduce new datastore interface

* refactor(api): refactor http and main layers

* refactor(api): refactor http and bolt layers

api/http/handler/users/admin_check.go

@@ -10,7 +10,7 @@ import (
 
 // GET request on /api/users/admin/check
 func (handler *Handler) adminCheck(w http.ResponseWriter, r *http.Request) *httperror.HandlerError {
-	users, err := handler.UserService.UsersByRole(portainer.AdministratorRole)
+	users, err := handler.DataStore.User().UsersByRole(portainer.AdministratorRole)
 	if err != nil {
 		return &httperror.HandlerError{http.StatusInternalServerError, "Unable to retrieve users from the database", err}
 	}