Support relative paths

[aviramha]

The filesystem feature bypasses (doesn't handle / reads locally) relative paths.
Recently we've had two cases where users asked for relative paths support.
The initial decision to ignore relative paths came from the notion that usually that'd be code and resources you'd want to get locally.
I think a good solution would be to get PWD from the remote process (available only when reading /proc/1 ?) or think of a better way to get it, then add in the config:

{
"feature": {
"fs": {
"read_only": ["$PWD/conf"]
}
}
}

i.e recognizing "$PWD" in the beginning as the marker, another option would be to add new config but that would be annoying.
The idea is that we don't alter current behavior (relative paths are still resolved locally by default)