Set cache_regions to True by default

[martindurant]

This seems to solve a number of aiobotocore redirect access issues, and aside from complexity, I don't see a downside.

[martindurant]

cc @Eugeny

One small caveat I have here, is the possibility of HEAD_BUCKET failing. I recebntly discovered that the following always succeeds (could be aiohttp rather than requests):

requests.head(f"https://{bucket}.s3.amazonaws.com").headers["x-amz-bucket-region"]

Do you think we should switch to this simpler form? It should be faster too, since it involves no auth.

Another specific thing that occurred to me: we should never use region caching together with endpoint_url, right?

[martindurant]

(cc @efiop , if interested)