chore: review other private files in CrowdSec exports #1567

What: other private files can live in the CrowdSec configuration folder, for example the certificate and key files that an http notification plugin points to with cert_path and key_path, or a custom file kept under a look-alike folder name. The export includes them as written.
Where: backend/internal/crowdsec/export.go (IsExportExcluded and the notification file selector in notifications_files.go).
Suggested approach: decide which paths referenced from notification settings should be left out of exports, and document the rest.
Severity: low. Found while planning #1551 (#1565).