datetime.datetime.utcnow() is deprecated since Python 3.12

[Lisias]

I'm running pywb on Python 3.12 nowadays, and I had noticed the following message on the logs now and then:

Deprecated since version 3.12: Use datetime.now() with UTC instead.

Researching about, I learnt that datetime.datetime.utcnow() is being deprecated - if I understood correctly, naive datetimes are going to be avoided.

Since is unavoidable that utcnow() will be removed from the Python's library, I consider prudent to prevent users from being caught by surprise in the foreseeable future.

[Lisias]

Hi, @tw4l .

I updated #914

WARCIO is now on version 1.7.5 where the option to get tz aware datetimes from the warcio.timeutils are implemented. I code reviewed my pull request to be sure these changes would not end up with mixed awareness on the same code. To the best of my knowledge, it will not.

I'm in the process of updating my appliance to the canon WARCIO, replacing my bootlegged interim one and then validate these pywb changes with it in a "production" environment.

I will update this issue with results in a way or another.

[Lisias]

Done. All my processes were rebooted using WARCIO 1.7.5 and PYWB with the patches from this pull request applied.

Everything still work as intended.