Add ability to configure proxy with env vars

[lubomir-haralampiev]

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Description

This PR adds a missing part of the workaround for the axios issue with corporate proxies.
request and axios as well provide the possibility to define proxy config via the environment variables HTTP_PROXY, HTTPS_PROXY and NO_PROXY. Currently the request wrapper doesn't interpret these env vars and doesn't create the needed https-proxy-agent. As a result the axios internal proxy logic is applied which causes the problems with many corporate proxies.

This PR adds this missing functionality.

References

#144
axios/axios#2072

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master