Improve SPDX import by generating generic PURLs when missing#2049

Monal-Reddy wants to merge 2 commits intoaboutcode-org:mainaboutcode-org/scancode.io:mainfrom

Monal-Reddy:fix-spdx-generic-purlMonal-Reddy/scancode.io:fix-spdx-generic-purlCopy head branch name to clipboard