Deliver notification of completed accession

[helrond]

Is your feature request related to a problem? Please describe.

Some donor organizations would like to know when a transfer has been completely accessioned so they can delete it from their local systems.

Describe the solution you'd like

Send an email to organization admin users when a transfer reaches the final accession status.

Additional context

Email notifications are currently delivered after initial transfer validation, and secondarily if a valid transfer is rejected by an appraisal archivist.