Add support for known network issues to be retryable

[cojenco]

Add support for known network issues to be retryable and align behavior across Storage SDKs.

Such errors as below are categorized as known network/transfer errors in gsutil and gcloud, see internal doc go/python-storage-retry-known-errors for more details

Known Network Errors(Retryable)	python storage clients	gcloud	gsutil
urllib3.exceptions.ProtocolError	Y	Y	Y
urllib3.exceptions.SSLError	N (need support)	Y	Y
urllib3.exceptions.TimeoutError	N (need support)	Y	Y
requests.exceptions.SSLError	Y	Y	Y

[tritone]

We should sync with gcloud storage team to confirm how this decision was made. Some of these errors can be permanent, so some caution is warranted.

[cojenco]

Synced with gcloud storage team, and as far as we understand, these errors are connection errors that are wrapped and re-raised by the urllib3 library. Very similar to the requests.exceptions.SSLError that is already being retried in our libraries. gsutil also has been retrying the above-mentioned errors since 2014.

I noticed that the gcloud team ran some tests, so I also reproduced the tests upon proposed changes. Experiment tests, system and conformance tests currently all pass.