auditable needs to be revised to be more general purpose

## What are the schemas that are affected by the issue
https://github.com/adobe/xdm/blob/d2a77b9ee7f8f600206b6e86f756064322e80d2d/schemas/common/auditable.schema.json

This seems to have been taken from a specific application use case but doesn't address other audit trail use cases, such as those used by Document Cloud in Sign.

Start by reading schemas/common/auditable.schema.json at the referenced revision and compare its fields with the audit-trail needs described for Document Cloud in Sign. Clarify the additional use cases and agree on the schema requirements before revising it; done means the schema supports general-purpose audit trails rather than one specific application.

Written by the indexing model from the issue text.