Take default date format from git config

[danielrainer]

It would be great if flog could use the log.date config from the relevant git config file by default, if no format is explicitly specified. This would automatically use peoples' preferred date format without having to configure anything for flog.

For example, I have log.date set to iso-local in my git config. At the moment, I would have to figure out flog's date configuration format in order to change the built-in default. The documentation and https://github.com/rbong/vim-flog/discussions/150 are nice to have, but so far I have not managed to figure out how I could get local times displayed by flog. Having that work automatically via the git config would be ideal.