fix: Strip Timezone from Timestamps in DB

[michael-genson]

What type of PR is this?

(REQUIRED)

• bug

What this PR does / why we need it:

(REQUIRED)

This PR explicitly removes time zones from datetime objects before storing them in the database, then re-adds the UTC timezone when retrieving them.

We do this because when using naive datetimes with postgres (which is what Mealie uses), postgres will convert datetimes to local time when storing. So, for instance, if we send this dt to postgres:

2024-10-03T14:34:32Z

And the postgres db timezone is in America/Chicago, it will store the dt as:

2024-10-03T08:34:32

Note that the time is not UTC, and the timezone info is now removed. So, once we retrieve it, we assume 2024-10-03T08:34:32 is UTC, and our timestamps are off.

Which issue(s) this PR fixes:

(REQUIRED)

Fixes #4288

Special notes for your reviewer:

Pretty simple fix, super annoying to debug.

Testing

(fill-in or delete this section)

I set my dev postgres db to Europe/Bratislava and Mealie as UTC and observed the issue in #4288. After this fix I no longer had any issues, and I manually verified the timestamps were correct (I also checked on SQLite just to make sure).