Add SPDX license data

[ofek]

In response to this comment by a maintainer expressing approval for license parsing functionality, this PR introduces an invoke task to update an enumeration encoded as a Python structure.

This setup is the same as what Hatchling does:

• https://github.com/pypa/hatch/blob/hatchling-v1.24.2/backend/scripts/update_licenses.py
• https://github.com/pypa/hatch/blob/hatchling-v1.24.2/backend/src/hatchling/licenses/supported.py

The parser itself and what the API should look like will be discussed in a separate PR.

The file may be generated by running: invoke licenses.update