## Purpose
The email template is made with the idea that they link to a document.
This change allows to customize the label of the button (currently,
"Open") to allow for a different action verb. Additionally, the
'document_title' parameter is renamed to 'link_label' to reflect that it
can link to other things than documents.
## Proposal
- [x] Email template `template.mjml` updated as proposed
- [x] Method `send_email()` updated
- [x] Translations updated