Show alerts again after dismiss (after a specified time)

I also like this idea! Lets target the 3.0.x first

Initial implementation to support time-based dismissible alerts.

Summary of changes:

New field: dismiss_period (integer, in hours), shown when “Dismissible” is enabled.

Backend:

Field added in baseFieldDefinitions()

Update hook (sitewide_alert_update_10301()) installs the field

Included in the form with conditional visibility

Frontend:

JavaScript updated to handle dismissal expiration via localStorage

Behavior:

Empty dismiss_period → permanent dismissal (default)

Value set → alert reappears after specified hours (e.g., 1, 24, 168)

Testing:

Set dismiss_period, dismiss alert, and verify it reappears after time

Backward compatible with existing alerts

Thanks to @alexis_mc for the contribution, one change was made in order to allow 0 hours value in the dismiss to allow a permanent solution.