Enable installing as a plugin in WordPress Playground

[JanJakes]

From https://wordpress.org/support/topic/trying-to-install-in-playground-so-i-cna-run-wp_cli/:

geting this error
 The SQLite Integration plugin is active, but the wp-content/db.php file is missing. Please deactivate the plugin and re-activate it to try again.
no matter what I do
see the issue here https://playground.wordpress.net/builder/builder.html#{%22landingPage%22:%22/wp-admin/%22,%22plugins%22:[%22sqlite-database-integration%22],%22preferredVersions%22:{%22php%22:%227.4%22,%22wp%22:%225.9%22},%22steps%22:[{%22step%22:%22login%22,%22username%22:%22admin%22}]}

We should make sure we get no errors when the SQLite Database Integration plugin is installed in WordPress Playground, and that any additional functionality or UIs work as expected.