feat(service_account): allow providing email when update a Service Account

Hi 👋

Small merge request to add email into the UpdateServiceAccountOptions struct for group service account PATCH endpoint (PATCH /groups/:id/service_accounts/:user_id).

See https://docs.gitlab.com/api/service_accounts/#update-a-group-service-account

I also took the liberty to update all GitLab documentation links in the file since most of them had dead anchors (bad # path).