Add SPDX style license and copyright boilerplate

Signed-off-by: Lukas Puehringer <[email protected]>

Author: lukpueh

tuf/api/metadata.py

@@ -1,3 +1,6 @@
+# Copyright New York University and the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
 """TUF role metadata model.
 
 This module provides container classes for TUF role metadata, including methods

tuf/api/serialization/__init__.py

@@ -1,3 +1,6 @@
+# Copyright New York University and the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
 """TUF role metadata de/serialization.
 
 This sub-package provides abstract base classes and concrete implementations to

tuf/api/serialization/json.py

@@ -1,3 +1,6 @@
+# Copyright New York University and the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
 """TUF role metadata JSON serialization and deserialization.
 
 This module provides concrete implementations to serialize and deserialize TUF