[bug#72577] [PATCH v2] services: agate: Change variable names and add system test.

[Christopher Howard <christopher@librehacker.com>]

Hi, I'm testing these patches in a qemu VM. I thought I should share that, if I explicitly set the certs field, I get an error:

```
/home/user/config.scm:52:35: error: (agate-configuration (content "/srv/gemini") (certs "/srv/gemini-tls") (log-ip? #f)): extraneous field initializers (certs)
```

Here is the config file:

```
;; -*- mode: scheme; -*-
;; This is an operating system configuration template
;; for a "bare bones" setup, with no X11 display server.

(use-modules (gnu))
(use-service-modules networking ssh web)
(use-package-modules screen ssh)

(operating-system
  (host-name "guix")
  (timezone "America/Anchorage")
  (locale "en_US.utf8")

  ;; Boot in "legacy" BIOS mode, assuming /dev/sdX is the
  ;; target hard disk, and "my-root" is the label of the target
  ;; root file system.
  (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (targets '("/dev/sda"))))
  ;; It's fitting to support the equally bare bones ‘-nographic’
  ;; QEMU option, which also nicely sidesteps forcing QWERTY.
  (kernel-arguments (list "console=ttyS0,115200"))
  (file-systems (cons (file-system
                        (device (file-system-label "my-root"))
                        (mount-point "/")
                        (type "ext4"))
                      %base-file-systems))

  ;; This is where user accounts are specified.  The "root"
  ;; account is implicit, and is initially created with the
  ;; empty password.
  (users (cons (user-account
                (name "user")
                (comment "Generic user")
                (group "users")

                ;; Adding the account to the "wheel" group
                ;; makes it a sudoer.  Adding it to "audio"
                ;; and "video" allows the user to play sound
                ;; and access the webcam.
                (supplementary-groups '("wheel"
                                        "audio" "video")))
               %base-user-accounts))

  ;; Globally-installed packages.
  (packages (cons screen %base-packages))

  ;; Add services to the baseline: a DHCP client and an SSH
  ;; server.  You may wish to add an NTP service here.
  (services (append (list (service dhcp-client-service-type)
			  (service agate-service-type
				   (agate-configuration
				    (content "/srv/gemini")
				    (certs "/srv/gemini-tls")
				    (log-ip? #f)))
                          (service openssh-service-type
                                   (openssh-configuration
                                    (openssh openssh-sans-x)
                                    (port-number 2222))))
                    %base-services)))
```

-- 
Christopher Howard