Support proxy for the CLI

[louis-bompart]

Currently, the Coveo CLI does not support restrictive proxy or the use of a custom proxy.

The goal of this idea is to change that and to support:

• NPM Proxy settings (proxy and https-proxy see)
• Environment Variables (HTTP_PROXY and HTTPS_PROXY)

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Internal tracking: CDX-548

[louis-bompart]

This requires us to drop AppAuthJS and rework from the ground-up the OAuth Client implementation of the CLI.
We do estimate this to be done by the end of September at the latest.

[louis-bompart]

Will be done in #491