Audit logging support

[shamus]

Is your feature request related to a problem? Please describe.

Audit logging is a requirement from most compliance standards (e.g. FedRAMP, PCI-DSS). Pinniped doesn't provide a way to meet these compliance requirements today.

Describe the solution you'd like

Just like the API Server has capabilities to provide Audit logs for all API requests, Pinniped components should provide auditable log for events such as login attempts, access denied events, session creation, termination etc.