Feature/3985 pm manifest support for copied files (#4075)

Subclass Manifest class for projects (ProjectManifest) to extend without impacting objects that use the Manifest class.

apps/dashboard/app/apps/ProjectManifest.rb

@@ -0,0 +1,5 @@
+class  ProjectManifest < Manifest
+  def files
+    manifest_options[:files] || []
+  end
+end

apps/dashboard/test/models/manifest_test.rb

@@ -138,7 +138,8 @@ class ManifestTest < ActiveSupport::TestCase
              metadata: { some_key: 'value' },
              new_window: false,
              caption: 'some caption',
-             invalid_key: 'invalid value'
+             invalid_key: 'invalid value',
+             files: ['file1', 'file2']
           }
 
     valid_manifest = <<~HEREDOC

apps/dashboard/test/models/project_manifest_test.rb

@@ -0,0 +1,24 @@
+require 'test_helper'
+
+class ProjectManifestTest < ActiveSupport::TestCase
+
+  test 'ProjectManifest writes files entries' do
+    opts = { files: ['file1', 'file2'] }
+
+    valid_manifest = <<~HEREDOC
+      ---
+      files:
+      - file1
+      - file2
+    HEREDOC
+
+    manifest = ProjectManifest.new(opts)
+
+    Dir.mktmpdir do |dir|
+      path = dir << '/manifest.yml'
+      manifest.save(path)
+
+      assert_equal valid_manifest, File.read(path)
+    end
+  end
+end