Split overlays into discrete functionality and test

- Closes #987

To make the overlays testable in isolation, and after discussion with
the TSC, removed host/time/source from overlay files.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

overlays/host/internal/warewulf.conf-static

@@ -0,0 +1,27 @@
+WW_INTERNAL: 43
+ipaddr: 192.168.0.1/24
+netmask: 255.255.255.0
+network: 192.168.0.0
+warewulf:
+  port: 9873
+  secure: false
+  update interval: 60
+  autobuild overlays: true
+  host overlay: true
+  syslog: true
+dhcp:
+  enabled: true
+  template: static
+tftp:
+  enabled: false
+nfs:
+  enabled: true
+  export paths:
+  - path: /home
+    export options: rw,sync
+    mount options: defaults
+    mount: true
+  - path: /opt
+    export options: ro,sync,no_root_squash
+    mount options: defaults
+    mount: false