Patch /TagInfo metadata container with information from the input HITS file

The `/TagInfo` metadata container written out by MC Overlay jobs is currently
based upon the container from the pre-mixed RDO file. This commit adds
any additional key-value pairs from the `/TagInfo` metadata container of the
input hard-scatter HITS file.

A more robust solution where the two input containers are somehow merged will
be sought, but this commit should fix most issues in the short term.


Former-commit-id: 1ead2cc9abd5ad03a73811b3625e52c3eecd1458