Validate migration files (#18203)

JSON Schema validation for data used by Gitea during migrations

Discussion at https://forum.forgefriends.org/t/common-json-schema-for-repository-information/563

Co-authored-by: Loïc Dachary <loic@dachary.org>

modules/migration/label.go

@@ -7,7 +7,7 @@ package migration
 
 // Label defines a standard label information
 type Label struct {
-	Name        string
-	Color       string
-	Description string
+	Name        string `json:"name"`
+	Color       string `json:"color"`
+	Description string `json:"description"`
 }