Track dgit and tag2upload adoption

It would be nice if trends.debian.net had a graph of adoption of dgit (for uploads) and tag2upload.

The way to detect this is to look at header fields in the .dsc:

1. No Dgit header: the package was uploaded solely as tarballs.
2. Dgit but not Git-Tag-Info: Uploaded with dgit.
3. Dgit and Git-Tag-Info: Uploaded with tag2upload.

Examples (all from trixie):

• Uploaded with tarballs only: http://deb.debian.org/debian/pool/main/d/dpkg/dpkg_1.21.22.dsc
• Uploaded with dgit: http://deb.debian.org/debian/pool/main/d/dgit/dgit_12.15.dsc
• Uploaded with tag2upload: http://deb.debian.org/debian/pool/main/o/openssh/openssh_10.0p1-7.dsc

I could possibly implement this but my Python isn't great. I'm hoping this description is good enough :-).

CC @spwhitton