honor configuration when sending emails

- Move the send_email() function into DistgitBugzillaSync as a method in
  order to access the configuration environment easily.
- Make whether or not emails are sent use the email.send_mails
  configuration option rather than the name of the configuration
  environment.
- Don't hard code the SMTP host.

Signed-off-by: Nils Philippsen <nils@redhat.com>

distgit_bugzilla_sync/default-config-files/configuration.toml

@@ -30,6 +30,7 @@ Reassigning to the new maintainer of this component.
 
 [email]
     send_mails = false
+    smtp_host = "bastion"
     from = "accounts@fedoraproject.org"
     notify_admins = [
         "root@localhost.localdomain",