Steps to reproduce

1. Configure SwiftMailer
2. Go to the backoffice
3. Create the new content
4. Send to review
5. Check email inbox

Result
You will receive an email (see attachment) which contains a button. The button's URL is:

/ez#/edit/%2Fapi%2Fezp%2Fv2%2Fcontent%2Fobjects%2F50/version/%2Fapi%2Fezp%2Fv2%2Fcontent%2Fobjects%2F50%2Fversions%2F3/eng-GB

The link does not contain a scheme and domain, therefore the button is completely useless.

Expected result
I want to get a clickable button.

Important note for v2
It seems that FlexWorkflow for v2 hasn't been rewritten correctly from v1. All links are generated like for the v1:
https://github.com/ezsystems/flex-workflow/blob/v3.0.1/lib/Core/SignalSlot/Slot/OnWorkflowUpdateSlot.php#L195
https://github.com/ezsystems/flex-workflow/blob/v3.0.1/lib/Core/SignalSlot/Slot/OnWorkflowUpdateSlot.php#L241