[day-04] add training schema

With this we can represent a traning program for a user.

lib/wabanex/training.ex

@@ -0,0 +1,28 @@
+defmodule Wabanex.Training do
+  use Ecto.Schema
+
+  import Ecto.Changeset
+
+  alias Wabanex.{Exercise, User}
+
+  @primary_key {:id, :binary_id, autogenerate: true}
+  @foreign_key_type :binary_id
+
+  @fields [:start_date, :end_date, :user_id]
+  @required_fields [:start_date, :user_id]
+
+  schema "trainings" do
+    field :start_date, :date
+    field :end_date, :date
+
+    belongs_to :user, User
+
+    timestamps()
+  end
+
+  def changeset(params) do
+    %__MODULE__{}
+    |> cast(params, @fields)
+    |> validate_required(@required_fields)
+  end
+end