Move API version to base_url

[kylemclaren]

i.e. the base_url should be https://api.replicate.com/v1 and v1 should be dropped in all client request paths. This is in line with the the JavaScript client, but also allows using a custom cog endpoint with the Replicate client (at least for prediction endpoints).

replicate-python/replicate/client.py

Lines 348 to 350 in d7ac942

	base_url = (
	base_url or os.environ.get("REPLICATE_BASE_URL") or "https://api.replicate.com"
	)