utils: move trace to utils

Without exposing `trace`, we can't set a target to enable tracing from
out of go-git.

Fixes: https://github.com/go-git/go-git/pull/916

plumbing/format/pktline/encoder.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/go-git/go-git/v5/internal/trace"
+	"github.com/go-git/go-git/v5/utils/trace"
 )
 
 // An Encoder writes pkt-lines to an output stream.

plumbing/format/pktline/scanner.go

@@ -4,7 +4,7 @@ import (
 	"errors"
 	"io"
 
-	"github.com/go-git/go-git/v5/internal/trace"
+	"github.com/go-git/go-git/v5/utils/trace"
 )
 
 const (