change output format of `--duration-float` to use users system/preferred language

[lucassabreu]

The --duration-float format used for showing only the total duration sum of time entries of a output is using "coding" format ("." for decimals and no character for thousands).

It should have support for formatting the number for the user preferred/system language to be easier to copy to other systems that may accept only numbers formatted to the users language.

Formatting a number to a language can be achieved using the package: https://pkg.go.dev/golang.org/x/text/number

Getting the users language is more complex because it depends on the users OS, preferably a new config/flag should be created to easy this problem, and also allow user to change the format "on the fly"