improvement: honor :priv in migration generator, and make it explic…

…itly configurable

closes #426

lib/migration_generator/migration_generator.ex

@@ -159,8 +159,15 @@ defmodule AshPostgres.MigrationGenerator do
     # Copied from ecto's mix task, thanks Ecto ❤️
     config = repo.config()
 
-    app = Keyword.fetch!(config, :otp_app)
-    Path.join([Mix.Project.deps_paths()[app] || File.cwd!(), "priv", "resource_snapshots"])
+    if snapshot_path = opts[:snapshots_path] do
+      snapshot_path
+    else
+      priv =
+        config[:priv] || "priv/#{repo |> Module.split() |> List.last() |> Macro.underscore()}"
+
+      app = Keyword.fetch!(config, :otp_app)
+      Application.app_dir(app, Path.join(priv, "resource_snapshots"))
+    end
   end
 
   defp create_extension_migrations(repos, opts) do

lib/repo.ex

@@ -39,6 +39,15 @@ defmodule AshPostgres.Repo do
   ```elixir
   %{type: :create, %{resource: YourApp.YourResource, action: :action}}
   ```
+
+  ## Additional Repo Configuration
+
+  Because an `AshPostgres.Repo` is also an `Ecto.Repo`, it has all of the same callbacks.
+
+  In the `c:Ecto.Repo.config/0` callback, you can configure the following additional items:
+
+  - `:tenant_migrations_path` - The path where your tenant migrations are stored (only relevant for a multitenant implementation)
+  - `:snapshots_path` - The path where the resource snapshots for the migration generator are stored.
   """
 
   @doc "Use this to inform the data layer about what extensions are installed"