Make record ID configurable

[jobara]

Is your feature request related to a problem?

At the moment the combinedRecord._id is string created by concatenating org.couch.db.user: and the username. It would be good if this entire id template could be configurable so that we could use a different or no prefix and provide a different value for the unique identifier portion. With the current setup, changing the username after the fact would cause potential conflicts with the future documents if someone tries to create a new account with either the old or modified username of an existing record.

Describe the solution you'd like

Make the combinedRecored._id template configurable.

[the-t-in-rtf]

@jobara, I think this was resolved in a recent pull?