Fix printing in php CLI context (like drush)

Problem/Motivation

When printing multiple documents (say commerce invoices, bulked at given time) with a background worker, a queue comes in handy. Generally when using entity_print from CLI context the resulting document should be the same as when printed through a web-call. This currently is not the case as symfony will provide "http://default" as the base request URL. As such printing engines will not include document relative styles.

Although an effort has already been made (sort of) for phpwkhtmltopdf to have absolute urls, sources and links, the fix isn't currently doing anything for prints in php CLI.

Steps to reproduce

Use drush or a queue worker initialized by cron to print an entity and observe the missing styles.

Proposed resolution

Commit my MR.