release: Add a MISSING_METALOGS hack to VMs

The packages for 15.0-RELEASE built without the bug fix needed to make
files created via @sample get properly listed in METALOG. Fix the
cloudware which contain @sample-using packages by adding the necessary
files to METALOG manually.

This should be reverted after the next full package build, and live on
only in releng/15.0.

Reviewed by: markj
MFC after: immediately (15.0-RC2)
Differential Revision: https://reviews.freebsd.org/D53797