Cache filtered CSV downloads for one hour

[paul-m]

The issue is that even if our infrastructure is set up to cache streaming CSV responses, DKAN tells it not to by defaulting to Cache-Control: private.

Luckily, we can use Drupal\common\CacheableResponseTrait to change the default on the existing controller, Drupal\datastore\Controller\QueryDownloadController. Setting a max age of one hour also tells this trait to use Cache-Control: public.

• Fixes minor bug in Drupal\common\CacheableResponseTrait.
• Leverages Drupal\common\CacheableResponseTrait to set max-age cache header to an hour.
• Updates Drupal\Tests\datastore\Unit\Controller\QueryDownloadControllerTest to check for the cache header.
• Updates other tests with @group so I can run them locally without running the whole test suite.

[dafeder]

Note the new @todo in the code; this should really be parameterized; we shouldn't assume 1 hour is right for all use cases.