Improve logging around the Signed PDF URL feature

[jakejackson1]

trafficstars

Description A user has reported Signed PDF URLs are expiring far earlier than was originally set. The problem is it is not easily reproducable, so I haven't been able to diagnose the issue.

I'd like to improve the debug log messages around the PDF signing feature so that this issue can be better tracked.

[jakejackson1]

Notify HS tag signed-pdf-logging on release