keywords: sample: Add METALOG entries for new files

This depends on a new lua function in pkg, see
https://github.com/freebsd/pkg/pull/2553 .

Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D53415

(cherry picked from commit 452309533805e8f4b7545f165c692cc37fe19b4c)