Updated select-aws-profile script to work with nushell version >= 0.94.2

[necromeo]

I've noticed that the select-aws-profile script doesn't work anymore as of nushell version 0.94.2. I've never used that script before, therefore I don't know from which version on it stopped working.

Exporting a function with the same filename is disallowed, hence the name change to main. As per the docs:

Exporting a command called main from a module defines a command named as the module.

Also, there were scoping issues. The env vars weren't being set. Adding the --env flag fixes that.