Make CC fetcher responsive to interrupts

[kkrugler]

During termination, we have long-running fetch threads that are busy downloading data from S3.

We need to check if we're interrupted and throw an exception. This might mean using an InputStream "bridge" to forward data from the AWS client in blocks, and check for interrupted state with each block.

We'd also want to check for interrupts before looking up URLs in our secondary index, etc.