[Feature Request] Allow _GIT_* variables to be passed as command-line args

[slw07g]

Allow _GIT_* variables to be passed as command-line args rather than having them set as environment variables.

https://github.com/arzzen/git-quick-stats/blob/71d414eb4a43ac32f939240b9975c958c9ace444/git-quick-stats#L176-L193

[igbanam]

The way I use this is almost like command line variables; but "pre" command line variables

_GIT_SINCE="2023-01-01" _GIT_UNTIL="2023-12-31" git-quick-stats -a

I think this keeps the git-quick-stats API clean and focused enough