Use the admin theme when editing or creating ECK entities by default

Problem/Motivation

The default value of the Use the administration theme when editing or creating ECK entities option on the Appearance page is false, which means that ECK forms are rendered using the frontend theme. I feel like since the progress in the Admin UI and JavaScript Modernisation Initiative, the Claro theme set as default admin theme and the rise in popularity of Gin theme this is no longer a sensible default. Maybe I'm biased since I have never had to integrate admin forms with custom frontend themes, but is this still a thing nowadays?

The node module has a similar option for their forms, Use the administration theme when editing or creating content. That option has been turned on by default for a long time when installing a site using the Standard profile.

Steps to reproduce

Install the module and visit the Appearance admin page. The option is turned off.

Proposed resolution

Turn on the Use the administration theme when editing or creating ECK entities by default for new installations.

Remaining tasks

Do it.

User interface changes

ECK forms will be rendered in the admin theme by default.