Account Migration

[alikindsys]

We should establish endpoints that allow for accounts to be migrated between different nicknames.

Those migrations can be triggered in the following cases:

• BLO-16
• BLO-17

Especial care should be taken for the second case, since we have no control over when a player can change their nicknames and nicknames by themselves aren't authoritative.

An account migration is the process for which an old username's data get transferred over to a new username. All the data associated with that username (and it's UUID) should be seamlessly transferred over to the new account.