Allow specifying relative path for custom flow.json locations

[jribbink]

Instructions

Issue To Be Solved

The VSCode Extension does not find the file if I specify a relative path for a custom flow.json location. This feels a bit misleading IMO because the flow.json will always be a descendent of the workspace root, so resolving relative paths from here seems somewhat intuitive. Not to mention it makes the repository impossible to clone & dependent on the user's particular directory structure.

We should be resolving the path using path.resolve to prevent this. This way both users trying to specify absolute and relative paths can be accommodated.

(Optional): Suggest A Solution

Use path.resolve 😛

(Optional): Context

Took me a while to debug why I couldn't specify my custom flow.json location