* Move SudoPrivilege out of SystemView
We only use this in token store and it literally doesn't work anything
that isn't the token store or system mount, so we should stop exposing
something that doesn't work.
* Reconcile extended system view with sdk/logical a bit and put an explanation for why SudoPrivilege isn't moved over
Move audit.LogInput to sdk/logical. Allow the Data values in audited
logical.Request and Response to implement OptMarshaler, in which case
we delegate hashing/serializing responsibility to them. Add new
ClientCertificateSerialNumber audit request field.
SystemView can now be cast to ExtendedSystemView to expose the Auditor
interface, which allows submitting requests and responses to the audit
broker.
