Add additional extracted TLS cert fields to the TLS monitor

[FrankieAtElastic]

Describe the enhancement:
The uptime monitor provided by Elastic Synthetics gives a nice UI and overview of TLS certificates being monitored, it would be great if we could extract more fields from the certificate, such as emailAddress, subjectAltDNS, subjectAltIP, SKI (public key hash)

Describe a specific use case for the enhancement or feature:
This would enable further insights into monitored certificates by having further visible fields.

• emailAddress: would grant a point of contact for alerts regarding certificate expiration, potentially allowing for notification to these owners
• SKI: Would provide a way of identifying the public key, as neither the cert fingerprint nor the serial number is unique to just the public key. The use case for this is more niche, and from a security perspective such as tracking re-use of private keys. A POC was made using 'the graph' that mapped the journey of a public key across different environments / CAs to track re-use and identify very old keypairs
• subjectAltDNS / subjectAltIP: Provides more context about where the certificate is useable

[FrankieAtElastic]

I will be happy to create a PR for this if it sounds good.