[request] --start --end values should consider local timezone

[dberardo-com]

when restating models with relative time values such as --start "2 weeks ago" for example, the current start_tstz variables are considering the beginning of the week in UTC time, but the is wrong because a relative time is to be interpreted in the eyes of a user and thus the start_tzts should consider the timezone information, at least as a optional input variable --tz for example.

inside the model everything can then be run in UTC but the start tstz should not be at 00:00+00 but rather at 00:00+0x meaning the beginning of the week where the use is located