Alerting: Implement setting of version message in convert API. (#114331)

Part 2 of adding version messages to the `alert_rule_version` able. This allows
setting the message via a header when using the Prometheus conversion API,
which can be useful for e.g. linking changes back to source control.

pkg/services/cloudmigration/cloudmigrationimpl/snapshot_mgmt_alerts_test.go

@@ -457,7 +457,7 @@ func createAlertRuleGroup(t *testing.T, ctx context.Context, service *Service, u
 		Rules:     rules,
 	}
 
-	err := service.ngAlert.Api.AlertRules.ReplaceRuleGroup(ctx, user, group, "")
+	err := service.ngAlert.Api.AlertRules.ReplaceRuleGroup(ctx, user, group, "", "")
 	require.NoError(t, err)
 
 	return group