Add quiet_assets to mute assets pipeline logging

Enabled in development environment only.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Explicitly enable quieten_assets in development

Improve discoverability of the configuration, in the case a developer
needs to re-enable asset pipeline logging.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1257 from opf/feature/quieten-assets-pipeline-logging

Add quiet_assets to mute assets pipeline logging