Create repo purls for GIT ecosystem ranges

**The CVE ID**
https://osv.dev/vulnerability/CVE-2019-25219

**Describe the data quality issue observed**
PURL entries are provided for the Debians. The Git repo could also have a PURL, in this case: `pkg:generic/github.com/chriskohlhoff/asio@asio-x-y-z` where the version comes from the tagging scheme used in that repo.

**Suggested changes to record**
Add a PURL for the Git repo. This supports the use case where the code is being packaged directly by the consumer, as opposed to installed via the Debian.