Fix newline handling in file, softlink, and ImportLink template functions

Use state-based routing instead of sentinel strings, so whitespace-trimming
syntax (e.g. `{{- file "name" -}}`) correctly creates all named files and
symlinks.

Fixes: #2118

Signed-off-by: Jonathon Anderson <janderson@ciq.com>
Co-authored-by: Christian Goll <cgoll@suse.com>
Signed-off-by: Jonathon Anderson <janderson@ciq.com>

overlays/ifupdown/internal/ifupdown_test.go

@@ -60,7 +60,6 @@ func Test_wickedOverlay(t *testing.T) {
 const expected_log string = `backupFile: true
 writeFile: true
 Filename: default
-
 # This file is autogenerated by warewulf
 auto wwnet0
 allow-hotplug wwnet0
@@ -69,7 +68,6 @@ iface wwnet0 inet static
   netmask 255.255.255.0
   gateway 192.168.3.1
   mtu 1500
-
 backupFile: true
 writeFile: true
 Filename: secondary