Add warning to log if SSL certificate is about to expire

### Problem Description

Currently if a website's SSL certificate rotates, Crawler can be caught off guard and start failing to sync. Ideally a user would swap both the website's certificate and Crawler's configuration at the same time, but there are situations where both are being managed independently even within a single organisation.

### Proposed Solution

To alleviate this, it would be useful for Crawler to check the expiration on the existing SSL cert and output a warning if it will expire in a week. This could be configurable but probably not required.