refactor: move prefix to config root level

Signed-off-by: Maria Eduarda Duarte <dudammduarte@yahoo.com.br>

pkg/objstore/client/factory.go

@@ -41,6 +41,7 @@ const (
 type BucketConfig struct {
 	Type   ObjProvider `yaml:"type"`
 	Config interface{} `yaml:"config"`
+	Prefix string      `yaml:"prefix" default:""`
 }
 
 // NewBucket initializes and returns new object storage clients.
@@ -82,16 +83,5 @@ func NewBucket(logger log.Logger, confContentYaml []byte, reg prometheus.Registe
 		return nil, errors.Wrap(err, fmt.Sprintf("create %s client", bucketConf.Type))
 	}
 
-	prefix := prefixFromConfig(bucketConf)
-
-	return objstore.NewTracingBucket(objstore.BucketWithMetrics(bucket.Name(), objstore.NewPrefixedBucket(bucket, prefix), reg)), nil
-}
-
-func prefixFromConfig(bucketConf *BucketConfig) string {
-	prefix, ok := bucketConf.Config.(map[interface{}]interface{})["prefix"]
-	if !ok {
-		return ""
-	}
-
-	return prefix.(string)
+	return objstore.NewTracingBucket(objstore.BucketWithMetrics(bucket.Name(), objstore.NewPrefixedBucket(bucket, bucketConf.Prefix), reg)), nil
 }