bin/57069: add '-f input_fmt' flag to date(1)

[jschauma%netmeister.org@localhost]

>Number:         57069
>Category:       bin
>Synopsis:       add '-f input_fmt' flag to date(1)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sat Oct 22 18:15:00 +0000 2022
>Originator:     Jan Schaumann
>Release:        NetBSD 9.3
>Organization:
	
>Environment:
Architecture: x86_64
Machine: amd64
>Description:

NetBSD's date(1) command currently requires the date to be set to be in
the format [[[[[[CC]yy]mm]dd]HH]MM[.SS]].  Aside from limiting the
date that can be set to be prior to the year 10,000, it also makes it
less flexible and requires the user to convert e.g., an epoch timestamp
into this format before setting the date instead of being able to e.g.,
run

date -f "%s" <epoch date>

Adding this option from e.g., FreeBSD would make that possible.

>How-To-Repeat:
Try to set the date to January 1st, 10,000.
Try to set the date to epoch 1234567890.

>Fix:

Consider taking FreeBSD's '-f' implementation.

>Unformatted: