aur: Change origin URL + add git origin + reduce disk writes
Simplify code for downloading packages index as gzip and deflate transfer-encodings are automatically decoded by requests, also do not stream response for a couple of megabytes.
Use https://aur.archlinux.org/packages/{package_name} as origin URL and also yield a git origin for each package repository URL.
Add more debug logs to track lister execution.
Migrated from D8383 (view on Phabricator)