[Improvement] Letting the developer initialize subscriber_key, publish_key and uuid for PNConfiguration during initialization

[JanluOfficial]

This commit changes the __init__ method of PNConfiguration() to optionally allow the developer to set subscriber_key, publish_key and uuid during initialization instead of setting them post-init. This lets developers initialize their PNConfiguration in one line, as opposed to the 4 lines it took previously, as shown currently by the official pubnub documentation.

[pubnub-ops-terraform]

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[stephenlb]

This looks safe, and backward compatible. It's pythonic and supports user initializing the config easily at instantiation. Allows end-user code reduction. I wonder if there is a way to use **kwargs to support member assignment at init()