fix: made bin/setup always run from the desired path

[rosshadden]

Impact: major
Type: bugfix

Issue

The general problem is that the find used in bin/setup is run from the PWD the script is run from.
The expected outcome is that bin/setup should only copy environment variables found within this project.

Right now running make init in reaction-platform copies the environment variables from every project's .env.example files into almost every .env file of every other project.
This is because in this case the find command used to find all .env.example files is being run from the platform directory, and thus all cloned projects within it are found by the find.

Solution

I made bin/setup cd to the root of the project before running the find.
This also prevents us from needing the $__dir variable we were using when referring to files within the script.

Testing

1. Run bin/setup from the root of this project (which is the only place it used to work from).
2. Run bin/setup from any other folder, such as reaction-platform or a folder that contains other reaction projects.

For both of these cases, verify that your working directory does not change. It shouldn't, because the cd happens within a function and is not expected to affect your shell directory.

[focusaurus]

Ouch. Good find and fix.