Streaming requests should be terminated if they get excessively backed up

As seen in MB-45844, streaming requests can get severely backed up if the client isn't able to / doesn't process the updates sent on the socket quickly enough. In that case 2 GB of ns_server memory was consumed by the process serving the streaming request alone.

It might work well to simply set a reasonable max heap size of say 100 MB on these processes. See: https://erlang.org/doc/man/erlang.html#process_flag_max_heap_size. 100 MB is ridiculously big, but it should prevent pathologically backed up clients from essentially causing a memory leak in ns_server.