Licenses export

[bxf12315]

Translate the license export functionality, which has already been implemented in version 1, to version 2.

[bxf12315]

The license export has two parts: the first part is obtaining all licenses, and the second part is generating the license CSV file. The second part can completely reuse version1's code. The first part needs to be reconsidered.
Based on my understanding over these days, I think there are currently two possible approaches:
1 Completely reuse version1's code, which means obtaining all license information through the SBOM source file.
2 Retrieve from version2's database.
Second approach currently has two issues:
2.1 First, we need to get all packages for an SBOM [similar functionality code], then right join with cpe_license_assertion and purl_license_assertion, followed by another right join with license.
2.2 Currently, I see that version2's license does not support the LicenseRef functionality.
Problems faced with approach two:
To obtain all licenses, too many tables need to be joined and two union operations are required.
Additionally, LicenseRef support needs to be implemented.