NEW NullDatabase (silverstripe#10016)

* NEW DatabaselessKernel to support operation without DB

This is required for GraphQL code generation in CI (without a working runtime database/webserver environment).
Context: silverstripe/silverstripe-graphql#388

* New --no-database option for sake

* Refactor to abstract class

* Apply feedback peer review

Co-authored-by: Aaron Carlino <unclecheese@leftandmain.com>
Co-authored-by: Maxime Rainville <maxime@silverstripe.com>

cli-script.php

@@ -4,6 +4,9 @@
 use SilverStripe\Control\CLIRequestBuilder;
 use SilverStripe\Control\HTTPApplication;
 use SilverStripe\Core\CoreKernel;
+use SilverStripe\ORM\DB;
+use SilverStripe\ORM\Connect\NullDatabase;
+use SilverStripe\Core\DatabaselessKernel;
 
 require __DIR__ . '/src/includes/autoload.php';
 
@@ -16,8 +19,17 @@
 // Build request and detect flush
 $request = CLIRequestBuilder::createFromEnvironment();
 
+
+$skipDatabase = in_array('--no-database', $argv);
+if ($skipDatabase) {
+    DB::set_conn(new NullDatabase());
+}
 // Default application
-$kernel = new CoreKernel(BASE_PATH);
+$kernel = $skipDatabase
+    ? new DatabaselessKernel(BASE_PATH)
+    : new CoreKernel(BASE_PATH);
+
 $app = new HTTPApplication($kernel);
 $response = $app->handle($request);
+
 $response->output();