Importing regression fix – support old exported Playground ZIPs (#1569)

## Motivation for the change, related issues

Closes #1543

Fixes importing older Playground exports via the `importWordPressFiles`
step.

Playground exports before changes from the Boot Protocol (#1398)
contained platform-level WordPress plugins and mu-plugins. The importer,
then, removed them and replaced them with the latest version freshly
sourced from the /wordpress directory.

However, after the Boot Protocol changes, Playground no longer includes
any platform-level plugins in the /wordpress directory. This means that
things like SQLite database integration were being removed from the
imported ZIP bundle but they were not restored.

This PR ensures the `0-sqlite.php` mu-plugin file will not be imported.
This way, we won't try to `require` files that the old export assumes to
exist but that do not exist anymore.

## Other ideas

I've initially tried removing the entire "remove & restore" files
mechanism, but that resulted in the following error:

![CleanShot 2024-07-03 at 11 28
37@2x](https://github.com/WordPress/wordpress-playground/assets/205419/10f5f1d4-7ba1-40c7-9cec-cf3ec13b8cf6)

It turned out every platform-level file **but** 0-sqlite.php was listed
for removal. Eventually I would still like to adjust the import flow to
remove this "remove & restore" dynamics and allow import bundles to ship
their own SQLite database integration plugin, but this PR will have to
do for now.

 ## Testing instructions

1. Export Playground as zip and import it again. Confirm this worked.
2. Run [this Blueprint that imports an older ZIP
bundle](https://playground.wordpress.net/builder/builder.html#{%22landingPage%22:%22/%22,%22preferredVersions%22:{%22php%22:%228.0%22,%22wp%22:%22latest%22},%22phpExtensionBundles%22:[%22kitchen-sink%22],%22features%22:{%22networking%22:true},%22steps%22:[{%22step%22:%22importWordPressFiles%22,%22wordPressFilesZip%22:{%22resource%22:%22url%22,%22url%22:%22https://kybernaut.cz/blueprints/pay-for-payment-playground.zip%22}},{%22step%22:%22login%22,%22username%22:%22admin%22,%22password%22:%22password%22},{%22step%22:%22installPlugin%22,%22pluginZipFile%22:{%22resource%22:%22wordpress.org/plugins%22,%22slug%22:%22woocommerce-pay-for-payment%22},%22options%22:{%22activate%22:true}}]})
and confirm it works

CC @vyskoczilova

packages/playground/blueprints/src/lib/utils/wp-content-files-excluded-from-exports.ts

@@ -11,6 +11,7 @@ export const wpContentFilesExcludedFromExport = [
 	'mu-plugins/sqlite-database-integration',
 	'mu-plugins/playground-includes',
 	'mu-plugins/0-playground.php',
+	'mu-plugins/0-sqlite.php',
 
 	/*
 	 * Listing core themes like that here isn't ideal, especially since