Added support for display_timestamp setting

[KaibutsuX]

Shows the generation timestamp in the resulting galleries and albums

This is helpful for automated/cron updates to see when the last run was

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.62%. Comparing base (eb86dec) to head (86633f0). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #524 +/- ## ======================================= Coverage 90.61% 90.62% ======================================= Files 24 24 Lines 2025 2026 +1 ======================================= + Hits 1835 1836 +1 Misses 190 190 ```

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[saimn]

Thanks!