services: Accept <inferior-package>s in lieu of <package>s.

* gnu/services/authentication.scm (fprintd-configuration)
(nslcd-configuration): Substitute file-like objects for package ones.
* gnu/services/cgit.scm (cgit-configuration, opaque-cgit-configuration):
Likewise.
* gnu/services/cups.scm (package-list?, cups-configuration): Likewise.
* gnu/services/dns.scm (verify-knot-configuration)
(ddclient-configuration): Likewise.
* gnu/services/docker.scm (docker-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration): Likewise.
* gnu/services/getmail.scm (getmail-configuration): Likewise.
* gnu/services/mail.scm (dovecot-configuration)
(opaque-dovecot-configuration): Likewise.
* gnu/services/messaging.scm (prosody-configuration)
(opaque-prosody-configuration): Likewise.
* gnu/services/monitoring.scm (zabbix-server-configuration)
(zabbix-agent-configuration): Likewise.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-configuration): Likewise.
* gnu/services/virtualization.scm (libvirt-configuration)
(qemu-guest-agent-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.

gnu/services/ssh.scm

@@ -283,7 +283,7 @@ The other options should be self-descriptive."
 (define-record-type* <openssh-configuration>
   openssh-configuration make-openssh-configuration
   openssh-configuration?
-  ;; <package>
+  ;; file-like object
   (openssh               openssh-configuration-openssh
                          (default openssh))
   ;; string
@@ -763,7 +763,7 @@ object."
 (define-record-type* <webssh-configuration>
   webssh-configuration make-webssh-configuration
   webssh-configuration?
-  (package     webssh-configuration-package     ;package
+  (package     webssh-configuration-package     ;file-like
                (default webssh))
   (user-name   webssh-configuration-user-name   ;string
                (default "webssh"))