Add proxy support to sysdig client stack

[tsimp06]

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These changes will allow the initializer to add a proxy at initialization of the client to add to the request session, for use for all requests in that instantiation.

[tembleking]

@tsimp06 Thank you for the submission, just a quick question: did you try to run the SDK with the environment variables HTTP_PROXY and HTTPS_PROXY configured? Maybe this would be enough instead of configuring the proxies as parameters.

[tsimp06]

@tsimp06 Thank you for the submission, just a quick question: did you try to run the SDK with the environment variables HTTP_PROXY and HTTPS_PROXY configured? Maybe this would be enough instead of configuring the proxies as parameters.

Yes, and while that works, we don't want to use the proxy for ALL requests, as we are using private endpoints for other requests in the same test.

[tsimp06]

@tembleking please see previous comment.