[SPIKE] Define/describe a migration plan/model for the dashboard

[jchartrand]

Plan how migrations would work, i.e, how issuers deploying this should upgrade as new code is added.

And specifically with the DB, Payload introduced database migrations in version 2 I think, whereas the admin dashboard uses version 1, so managing database migrations needs to be thought through.

This is another compelling reason to move data CRUD to a restful service (see #9 and #10). Changes would be made by defining a new version of the API, providing a clearer and more consistent contractual definition of change, and allowing implementations to fulfill their side of the contract as best matches their implementation.