Add date support for Retry-After header in maintetance mode

[theeldarka]

Option "retry" supports only numeric, but header Retry-After can be a date, not only a delay in seconds.
I want to start php artisan down --retry="Tue, 03 May 2022 21:00:00 GMT"

Retry-After header documentation: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After

Problem here:

framework/src/Illuminate/Foundation/Console/DownCommand.php

Line 148 in 6e0fb37

return is_numeric($retry) && $retry > 0 ? (int) $retry : null;