NMS-16317: Minion Container: Add way to overlay config files

[mershad-manesh]

Expanding the Minion helm chart by adding a configmap that places files under /minion-etc-overlay folder

Example:
$ cd minion $ echo "Hello World" > etc/hello.txt

Limitations:

• Only supports flat layout, we don't support folders/subdirectories (This won't work etc/test_folder/test.txt)
• The configMap cannot be bigger than 1MB
• We do not support any compression
• Support latests Container images

[mmahacek]

Once this is tested, minion/README.md should be updated to include a note about adding the overlay directory.

[ProjectJYL]

Works for me!