Specify a user agent for OSV.dev

[spencerschrock]

The Scorecard weekly cron makes many API calls to osv.dev. The OSV team asked if we specify a unique user agent, and we don't.
It would be good to set one. There is a RequestUserAgent variable we can set in the osv package. https://pkg.go.dev/github.com/google/osv-scanner@v1.7.1/pkg/osv#pkg-variables.

osv-scanner sets user agents like:
osv-scanner/1.7.1 (where v1.7.1 is the osv-scanner version)

It would be nice if scorecard set a user agent for both our CLI (scorecard/{version}) and our weekly cron workers (scorecard-cron/{version}). We have version info available to the various binaries via version.GetVersionInfo