Add ERB eval so we can use credentials

test/configuration_test.rb

@@ -26,4 +26,9 @@ class ConfigurationTest < ActiveSupport::TestCase
     configuration = Mrsk::Configuration.new(@config.tap { |c| c[:registry].merge!({ "server" => "ghcr.io" }) })
     assert_equal "ghcr.io/dhh/app:123", configuration.absolute_image
   end
+
+  test "erb evaluation of yml config" do
+    configuration = Mrsk::Configuration.load_file Pathname.new(File.expand_path("fixtures/deploy.erb.yml", __dir__))
+    assert_equal "my-user", configuration.registry["username"]
+  end
 end

test/fixtures/deploy.erb.yml

@@ -0,0 +1,11 @@
+service: app
+image: dhh/app
+servers:
+  - 1.1.1.1
+  - 1.1.1.2
+env:
+  REDIS_URL: redis://x/y
+registry:
+  server: registry.digitalocean.com
+  username: <%= "my-user" %>
+  password: <%= "my-password" %>