add username field, make it main log-in method

priv/repo/migrations/20210622112812_create_users_auth_tables.exs

@@ -5,6 +5,7 @@ defmodule PokemonCouture.Repo.Migrations.CreateUsersAuthTables do
     execute "CREATE EXTENSION IF NOT EXISTS citext", ""
 
     create table(:users) do
+      add :username, :citext, null: false
       add :email, :citext, null: false
       add :hashed_password, :string, null: false
       add :confirmed_at, :naive_datetime
@@ -12,6 +13,7 @@ defmodule PokemonCouture.Repo.Migrations.CreateUsersAuthTables do
     end
 
     create unique_index(:users, [:email])
+    create unique_index(:users, [:username])
 
     create table(:users_tokens) do
       add :user_id, references(:users, on_delete: :delete_all), null: false