Option to enter expiry period in days instead of seconds

The pipeline is reporting errors in PHPCS and PHPUnit, but they are not related to this change.

LGTM

Will wait for the other maintainers to chime in but personally I'm not keen on this.
If we must do it, would prefer the input to be something like interval field where there's two fields inline one number, and one interval (e.g. days, weeks, seconds, minutes etc)

I personally don't agree with this. The checkbox makes the UX confusing (you're checking a checkbox and then entering a number of days into a field that says seconds)

If this was a form that required interaction more often than once in a blue moon I think it'd make sense to improve the UX but this is just something you could calculate in the background (e.g google "5 days in seconds" and copy the value).

I understand the concern. I've had a look though and when installing, by default it's seconds:

If you choose days, the form changes to:

and the Expiry seconds becomes readonly.

Sorry, I missed the second field. I still don't think this is something we want to or need to support.