If credentialz is enabled, other credential configuration should be disabled

[dplore]

For the operational use case where a 'security actor' is in control of credentials and a 'second actor' is in control of all other device configuration, it is desirable that the 'second actor' can perform gNMI SetRequest replace operations without overwriting or conflicting with gNSI managed state. One place where there is overlap between gNMI managed config and gNSI is credentialz.

To enable this use case, should we introduce a method in gNSI which will instruct the device to disable configuration of credentials via gNMI? When disabled, should the device silently ignore replace requests for paths within /openconfig-system:system/aaa/authentication/config?

Thoughts?