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

[Christopher Howard]

Another little detail perhaps worth noting: the guix documentation specifies 
that if no valid key and certificate is available, then Agate will try to 
generate them on its own. However, if you attempt to go this route, you get an 
error:

```
2024-08-16 10:58:21 No keys or certificates were found in the given directory.
2024-08-16 10:58:21 Specify the --hostname option to generate these 
automatically.
```

But there does not appear to be a hostname field available to 
agate-configuration, or at least it is not documented. Only the "hostnames" 
field for virtual hosts.

-- 
Christopher Howard