Add SPDX license list version to license data dumps

[pombredanne]

This would be useful

[AyanSinhaMahapatra]

This is finished, see https://scancode-licensedb.aboutcode.org/help.html

The footer text in all pages looks like this now:

Designed and built by [nexB](https://www.nexb.com/). Licensed under the [Creative Commons Attribution License 4.0 (CC-BY-4.0)](https://scancode-licensedb.aboutcode.org/cc-by-4.0.html).

Generated with [ScanCode toolkit](https://github.com/nexB/scancode-toolkit) 32.0.0rc1 on 2023-01-18.

SPDX Licenses list version: 3.19