Add leave organization hyperlink on the project/group access granted email

Summary

Follow up for #465861 (closed)

Add an hyperlink to leave the organization on the project/group access granted email.

Implementation Guide

• Update member_access_granted_email.text.erb and member_access_granted_email.html.haml content accordingly:

If this was a mistake, you can leave the [group/project name] group/project or the [organization name] organization.

• Update the specs (e.g. notify_spec.rb)
• Must be behind ui_for_organization feature flag.

Note: Clicking on the group/project/organization name should redirect the user to the leave URL for that entity.