Make map encoding configurable

[a-nassim]

I wanted to try the SQLite JSONB format, i.e. JSON stored as a BLOB instead of a TEXT.
I was able to do so by specifying the :blob type instead of :map in a migration.

defmodule Migration do
  @moduledoc """
  Updates resources based on their most recent snapshots.

  This file was autogenerated with `mix ash_sqlite.generate_migrations`
  """

  use Ecto.Migration

  def up do
    create table(:resources, primary_key: false) do
      # add :my_map, :map, null: false <- generated line
      add :my_map, :blob, null: false #  <- edited line
      add :id, :bigserial, null: false, primary_key: true
    end
  end

  def down do
    drop table(:resources)
  end
end

It would be convenient if we could use :map in migrations, configuring :blob just once for the adapter, similar to how it is done in the Postgres adapter. TEXT could still be the default.

What do you think?

[warmwaffles]

I think mimic'ing how it is done with the postgres adapter is a good idea. Since this feature was added to SQLite 3.45, (we are at 3.49), we will need to have the default be what it is now and set a timeline on when it will be swapped to be jsonb by default.

[warmwaffles]

Feel free to open a PR for it! I don't have time this week to add it.