#9739 Set proxy setting from environment variables, falling back to p…

[wozzo]

Implements #9739 allowing the proxy target to be set using environment variables and falling back to package.json if none exists.

Tested by running a project with the change applied.

1. Ran with no proxy environment variable, but with proxy in package.json. Result: Used proxy from package.json
2. Ran with proxy environment variable and package.json. Result: Used proxy from environment variable
3. Ran with proxy environment variable and none in package.json. Result: Used proxy from environment variable

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[wozzo]

CLA completed

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Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

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Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[wozzo]

Still needed.