Use relative paths in Greengrass config.yaml

[kucnavya]

Greengrass config.yaml uses absolute paths right now as relative paths don't seem to work. Root cause and fix the issue.

https://github.com/aws-greengrass/aws-greengrass-snap/blob/CustomSnap/examples/aws-greengrass-config/local-files/shared-files/config.yaml#L3-L4