Resume read rows stream when `google.api_core.exceptions.Unknown: None No status received` encountered

[tswast]

See: apache/beam#15185 (comment)

In offline discussion, this might reflect the HTTP/2 stream being closed unexpectedly.

https://github.com/grpc/grpc/blob/bc09e792c81da1fd5dcafeff84ce5c6c41aa83c1/src/core/lib/surface/call.cc#L1089-L1094

I believe we should treat this the same way we do transport-level errors in the REST clients and retry/resume by default.