Add additional tags/labels for x509 input metrics

[lawliet89]

Feature Request

The x509 input plugin should include additional labels for the metrics.

Proposal:

Include the following additional information for tags/labels:

• SAN
• Serial Number

The following would be nice to have, but might be too much information and perhaps can be optional:

• Key type
• Issuer CN
• Issuer Serial

Current behavior:

Does not include the tags/labels.

Desired behavior:

Include the tags/labels.

Use case:

This will allow for additional ways to disambiguate certificates which can be different for the same CN and source.