[#1671] Use fmt.Appendf where warranted

Fix gopls warnings:
```
cmd/frostfs-adm/internal/modules/morph/config/config.go:68:20-64: Replace []byte(fmt.Sprintf...) with fmt.Appendf
````

gopatch:
```
@@
var f expression
@@
-[]byte(fmt.Sprintf(f, ...))
+fmt.Appendf(nil, f, ...)
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

scripts/populate-metabase/internal/populate.go

@@ -31,13 +31,10 @@ func PopulateWithObjects(
 
 	for range count {
 		obj := factory()
-
-		id := []byte(fmt.Sprintf(
-			"%c/%c/%c",
+		id := fmt.Appendf(nil, "%c/%c/%c",
 			digits[rand.Int()%len(digits)],
 			digits[rand.Int()%len(digits)],
-			digits[rand.Int()%len(digits)],
-		))
+			digits[rand.Int()%len(digits)])
 
 		prm := meta.PutPrm{}
 		prm.SetObject(obj)