Monitoring AppRole Secret Expiration

[eugenedavis-tomtom]

Monitoring the age and expiration of an AppRole secret id would help with managing AppRole authentication usage.

It has a relatively similar structure to the metadata for a KV2 secret, so it should be possible to subclass the ExpirationMetadata class - only the update_metrics method need be different, and realistically it could be done with an f-string for the path as the only difference per subclass.

[eugenedavis-tomtom]

Metrics should also reflect approle vs secret