Introduce a separate controller for collection entropy config

which opens the door to rendering turbo frames in the responses to
collection edits.

test/controllers/collections/entropy_configurations_controller_test.rb

@@ -0,0 +1,17 @@
+require "test_helper"
+
+class Collections::EntropyConfigurationsControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in_as :kevin
+    @collection = collections(:writebook)
+  end
+
+  test "update" do
+    put collection_entropy_configuration_path(@collection), params: { collection: { auto_close_period: 1.day, auto_reconsider_period: 2.days } }
+
+    assert_equal 1.day, @collection.entropy_configuration.reload.auto_close_period
+    assert_equal 2.days, @collection.entropy_configuration.reload.auto_reconsider_period
+
+    assert_redirected_to edit_collection_path(@collection)
+  end
+end