feat(o365_mu): add groupMail for Groups
Created by: stavamichal
- groups now need to consume a new attribute groupMail to be correctly processed on the server site. This attribute is counted from list of o365 group mails. We take the one with domain 'group.muni.cz' or any other if there is no email with such domain
- change for gen and send script
- cache for groups will be different, all groups will need to be updated at the first run (new column)