Change Ecto timestamps from inserted_at to created_at

When you generate a schema or migration that will create database tables your Elixir app will utilize there will usually be a call to timestamps/0 in the newly generated file, if not you can add it manually.

The timestamps function will add timestamp columns to your table to track when records are created and updated. By default this will create columns intserted_at and updated_at, but you can override these column names to suit your needs by passing a keyword list argument containing the column you want to override and the column that should take its place. Example:

  def up do
    create table("weather") do
      add :city,    :string
      add :temp_lo, :integer
      add :temp_hi, :integer
      add :prcp,    :float

      timestamps(inserted_at: :created_at, updated_at: :updated_time)