Support for record timestamp based profile overrides in a dataset

### What are the schemas that are affected by the issue
Profile Schemas.
Auditable Schema

### Name of the field added
xdm:sourceLastModifiedDate

### Description of the field
This timestamp field is the timestamp of the record on the customer system. Represents the timestamp on the customer system.
For example, in the case of a CRM record, this will be the timestamp of last modification of the record.

### Reason for the addition of a new field
There is no field that captures a timestamp on the customer system. The current timestamps under repo capture the repository timestamps (internal sources).

### Ref: https://jira.corp.adobe.com/browse/CORE-32522

Locate the Profile Schemas and Auditable Schema definitions and inspect how existing repository timestamps are represented. Add xdm:sourceLastModifiedDate with the stated customer-system timestamp meaning to the affected schemas, then verify that the schema definitions remain valid.

Written by the indexing model from the issue text.