Add CertObserver to the list of monitors

[Jonas Meller]

Hi,

I would appreciate it if CertObserver (https://certobserver.com/) could be added to the list of monitors.

CertObserver provides a free, quick CT search tool (https://certobserver.com/ct-search), as well as CT monitoring as part of its paid functionality.

We verify STH signatures and check that the STH root hash matches the Merkle root we calculate from the entries fetched up to that tree size.

Best regards,
Jonas Meller