User, tags and hashed password can be inserted/updated at once,
increasing the performance of the storage backend - both for mnesia
and khepri.

`khepri:find/2` expects a path and condition. We may want to
pre-populate the condition in the future, but for now - at least it
works.

In particular which node is picked while trying to make the Khepri
cluster match the Mnesia one.

... when a Mnesia-based node joins a Khepri-based node.