ament_copyright does not recognize REUSE-compliant copyright headers

[REUSE](https://reuse.software/) from the [Free Software Foundation Europe](https://fsfe.org/) uses the following style as a copyright header (see also https://reuse.software/faq/)
```
# SPDX-FileCopyrightText: [year] [copyright holder] <[email address]>
#
# SPDX-License-Identifier: [identifier]
```
The copyright and the license are both not recognized by ament_copyright (resulting in a "could not find copyright notice" error).
I think this is a valid way to specify the license and it has been already adopted by many projects (e.g. large parts of the Linux kernel). Therefore, it would be great if ament_copyright would correctly recognize this so that developers of ROS packages can also use these REUSE-compliant headers.