osbase/logtree.LeveledLogger -> go/logging.Leveled

This factors out the common leveled logger interface out of the logtree.
We want to use the same interface outside of logtree/supervisor usage
within the resolver code, which will be exposed to clients.

Change-Id: I299e76d91e8cefddf8f36f1e58432418c4694df2
Reviewed-on: https://review.monogon.dev/c/monogon/+/3411
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/logtree/logtree.go b/osbase/logtree/logtree.go
index c20681d..b6f8a06 100644
--- a/osbase/logtree/logtree.go
+++ b/osbase/logtree/logtree.go
@@ -21,6 +21,7 @@
 	"strings"
 	"sync"
 
+	"source.monogon.dev/go/logging"
 	"source.monogon.dev/osbase/logbuffer"
 )
 
@@ -52,7 +53,7 @@
 	tree *LogTree
 	// verbosity is the current verbosity level of this DN/node, affecting .V(n)
 	// LeveledLogger calls
-	verbosity     VerbosityLevel
+	verbosity     logging.VerbosityLevel
 	rawLineBuffer *logbuffer.LineBuffer
 
 	// mu guards children.