correct **kwargs documentation in docstrings

[skarzi]

Hi 👋

first of all thanks for maintaining and developing this great SDK!

This PR fixes kwargs documentation in Args section of docstrings.
According to Google Python Style Guide *args and **kwargs should be documented in Args section using following format:

If a function accepts *foo (variable length argument lists) and/or **bar (arbitrary keyword arguments), they should be listed as *foo and **bar.

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[skarzi]

@googlebot I signed it!

[lahirumaramba]

Thank you @skarzi ! LGTM
Adding @egilmorez as this might update reference docs.