Alerting: Rule Modify Export APIs (#75322)

* extend RuleStore interface to get namespace by UID
* add new export API endpoints
* implement request handlers
* update authorization and wire handlers to paths
* add folder error matchers to errorToResponse
* add tests for export methods

pkg/services/ngalert/api/errors.go

@@ -11,6 +11,9 @@ import (
 
 var (
 	errUnexpectedDatasourceType = errors.New("unexpected datasource type")
+
+	// errFolderAccess is used as a wrapper to propagate folder related errors and correctly map to the response status
+	errFolderAccess = errors.New("cannot get folder")
 )
 
 func unexpectedDatasourceTypeError(actual string, expected string) error {
@@ -34,5 +37,8 @@ func errorToResponse(err error) response.Response {
 	if errors.Is(err, ErrAuthorization) {
 		return ErrResp(401, err, "")
 	}
+	if errors.Is(err, errFolderAccess) {
+		return toNamespaceErrorResponse(err)
+	}
 	return ErrResp(500, err, "")
 }