Support for platform in client.images.api.push

[Khushiyant]

API version v1.48 accepts platform argument as parameter to be passed to /images/{name}/push but it is not implemented in image.py.

Below function should accept platform i.e JSON-encoded OCI platform to select the platform-variant to push:

def push(self, repository, tag=None, stream=False, auth_config=None,
             decode=False):