WSOD on custom block creation / listing if config translation enabled

Problem/Motivation

1. Install Drupal with Standard profile
2. Enable Configuration translation module
3. Go create a custom block, it will be created, but you get a 500 error response page (with the green message and nothing else)
4. Reload the (list) page that you are on and it will still whitescreen

Error in error log:

Uncaught PHP Exception Drupal\\Core\\Entity\\Exception\\UndefinedLinkTemplateException: "No link template "drupal:config-translation-overview" found for the "custom_block" entity type" at ...../drupal/core/lib/Drupal/Core/Entity/Entity.php line 178

The problem is the custom block listing uses a list builder originally designed for config entities and the config_translation code assumes it will have a config translation link template. So breaks.

Proposed resolution

Only alter the entity operations if the entity has a link template for config translation.

Remaining tasks

Add tests.

User interface changes

None.

API changes

None.