Add antispam plugin config for dovecot to trigger rspamd learning whenever message is moved from inbox to spam

roles/mailserver/files/etc_dovecot_conf.d_90-antispam.conf

+plugin {
+    antispam_backend = pipe
+    antispam_spam    = Junk
+    antispam_trash   = Trash
+    antispam_mail_sendmail = /usr/bin/rspamc
+    antispam_mail_spam     = learn_spam
+    antispam_mail_notspam  = learn_ham
+    antispam_mail_sendmail_args = -h;localhost:11334;-P;q1
+}

roles/mailserver/tasks/dovecot.yml

     - 10-auth.conf
     - 10-mail.conf
     - 10-master.conf
+    - 90-antispam.conf
     - auth-sql.conf.ext
   notify: restart dovecot