Allow preview links to be restricted to specific entity types and bundles.

Looking really good, just one super minor nit.

+++ b/src/Access/PreviewEnabledAccessCheck.php
@@ -0,0 +1,83 @@
+   * Check if the entity type and bundle are allowed.

Nit: allowed > enabled

.

LGTM

+++ b/preview_link.post_update.php
@@ -0,0 +1,15 @@
+  $config = \Drupal::configFactory()->getEditable('preview_link.settings');

do we need to check the installed version here so this only runs on existing sites?

+++ b/preview_link.post_update.php
@@ -0,0 +1,15 @@
+function preview_link_post_update_install_config() {

This needs to update hook because we are adding the new schema.

if updb installs the new schema

updb doesn't install new schema.

wouldn't I want a post update here to ensure the schema is present before adding the new config

schema should be valid before running post-update hooks. As we are adding the new schema that means after updating the codebase site will have invalid schema so it should be fixed by hook_update_N.

Thanks!