Add instance title to the subject and body of the email notifications
The #29024 introduced the instance title. It would be very helpful to have this information in the email notifications subject and body for people who maintain multiple Foreman instances. It may not be a bad idea to have also Foreman instance ID (UUID stored as another setting) in the footer of all email notifications too.
There is a subject prefix in email settings that is used in subject in
every email. It was only way to recognise a right foreman instance from
many instances. This PR adds a header X-Foreman-ID that includes a
instance_title from Settings, if it's set. Also, this PR adds a footer
for every email where is information about instance_title and
identifier (UUID) of Foreman instance.