Refactor wwctl <node|profile> edit and fix bugs

`wwctl node edit` appears to not be working properly since MergeNode. This
refactor, partly towards #918, resolves the issues with `node edit` and updates
`profile edit` to match.

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

internal/pkg/node/constructors.go

@@ -3,6 +3,7 @@ package node
 import (
 	"os"
 	"sort"
+	"syscall"
 
 	warewulfconf "github.com/warewulf/warewulf/internal/pkg/config"
 	"github.com/warewulf/warewulf/internal/pkg/wwlog"
@@ -10,6 +11,10 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
+func CanWriteConfig() bool {
+	return syscall.Access(warewulfconf.Get().Paths.NodesConf(), syscall.O_RDWR) == nil
+}
+
 /*
 Creates a new nodeDb object from the on-disk configuration
 */