Fix reading of deleteTrashFoldersMaxAllowedTime

The configuration value deleteTrashFoldersMaxAllowedTime was previously
looked up by passing the config key name into
getTrashFoldersMaxAllowedTimeFromConfig(), which caused the method to
re-read configuration instead of using the already available plugin
config. This leads to the value not being interpreted correctly.

Update the call site to pass the resolved config string from the plugin
Config instance, ensuring the duration is parsed from the expected
source. Expose the default trash folder timeout constant so tests can
verify fallback behavior.

Change-Id: I7f39eb50a79423211dd99231f4859f775a0c2628