fix(emailTemplate): use instance Name instead of Url in subject

[solracsf]

Summary

A lot of anti-spam systems doesn't like plain URLs on the email subject (ex.: Orange in France) and place those emails on Junk folder. Use instance Name instead (URL is kept on email body).

Before

Email address for Carroll, Mathieu changed on https://cloud.my-personal-cloud.org/

After

Email address for Carroll, Mathieu changed on My Personal Cloud

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)