adding proxy support to SDK

[fatihkurtoglu]

Pull Request Summary

• Adding proxy support to SDK Client initialization. Now users can pass proxies, cert and verify parameters to their requests

    proxies = { 'https': 'http://10.10.1.10:1080' }
    
    client = scaleapi.ScaleClient(
                api_key="YOUR_API_KEY_HERE",
                proxies=proxies,
                cert='/path/client.cert',
                verify=True
            )

Description

Please include a summary of the changes. Please also include the relevant context and motivation. List any dependencies and assumptions that are required for this change.

How did you test your code?

Which of the following have you done to test your changes? Please describe the tests that you ran to verify your changes.

• Created new unit tests in tests/ for the newly implemented methods
• Updated existing unit tests in tests/ to cover changes made to existing methods

Checklist

Please make sure all items in this checklist have been fulfilled before sending your PR out for review!

• I have commented my code in details, particularly in hard-to-understand areas
• I have updated Readme.rst document with examples for newly implemented public methods
• I have reviewed Deployment and Publishing Guide for Python SDK document
• I incremented the SDK version in _version.py (unless this PR only updates the documentation).
• In order to release a new version, a "Release Summary" needs to be prepared and published after the merge

[jonathanfeng-scale]

LGTM

[shaun-scale]

Seems straightforward, thank you for implementing + documenting!