feat: allow retrieving the action from an action error (#538)

When an action error occurs within the action waiter utilities, we are
missing information about the related action that failed. With this
change, we can now retrieve the action that triggered the failure after
casting the error to an action error.

hcloud/action.go

@@ -54,6 +54,13 @@ const (
 type ActionError struct {
 	Code    string
 	Message string
+
+	action *Action
+}
+
+// Action returns the [Action] that triggered the error if available.
+func (e ActionError) Action() *Action {
+	return e.action
 }
 
 func (e ActionError) Error() string {
@@ -65,6 +72,7 @@ func (a *Action) Error() error {
 		return ActionError{
 			Code:    a.ErrorCode,
 			Message: a.ErrorMessage,
+			action:  a,
 		}
 	}
 	return nil