Redirection plugin: Optionally generate redirects without trailing slashes

[stooit]

The queue generator for the redirection plugin will retrieve redirects "as-is", which generally appear to have trailing slashes on the source URL: https://github.com/quantcdn/wordpress/blob/develop/plugins/quant/src/seed/RedirectionBatch.php

We should optionally allow for this process to strip the trailing slash to keep redirects clean and URLs aligned to the process already in place for content routes.

[stooit]

This is enforced in #18 as consistent content routes are required for redirect monitoring to function as expected.