repository: Increase index size for repo version 2

A compressed index is only about one third the size of an uncompressed
one. Thus increase the number of entries in an index to avoid cluttering
the repository with small indexes.

internal/repository/repository.go

@@ -698,6 +698,9 @@ func (r *Repository) SearchKey(ctx context.Context, password string, maxKeys int
 	} else if err != nil {
 		return errors.Fatalf("config cannot be loaded: %v", err)
 	}
+	if r.Config().Version >= 2 {
+		r.idx.markCompressed()
+	}
 	return nil
 }