Add object compression support (#6292)

Add support for streaming (golang/LZ77/snappy) compression.

cmd/gateway/b2/gateway-b2.go

@@ -840,3 +840,8 @@ func (l *b2Objects) DeleteBucketPolicy(ctx context.Context, bucket string) error
 	logger.LogIf(ctx, err)
 	return b2ToObjectError(err)
 }
+
+// IsCompressionSupported returns whether compression is applicable for this layer.
+func (l *b2Objects) IsCompressionSupported() bool {
+	return false
+}