-rename isSource() to isValidSource() and rewrote content
- tested with latest backp's git-mirror tool v0.14.1
- documentation tip with SSH keypair

using **kwargs instead

cache storage only store the current group

so we can inject Authorization header when needed.
Added hard coded request timeout : would be too bad is the script hangs
forever...

Also fixed a regex issue for gh's api pagination

Would work only with github sources

Process only the repo from the only list.