Implement 'Date' header

[Luukdegram]

HTTP 1.1 describes the requirement of having to include a Date header, containing the current date in GMT. We can use the following format for this:
Date: Fri, 31 Dec 1999 23:59:59 GMT

Currently, there's an open PR on Zig's std: #9040 that we could leverage for this.
But we will have to build upon it to get the current day of the week. (mon, thu, etc)