Updating rdkafka to include fetch.queue.backoff.ms patch

[bitemyapp]

Cf.

• Consumer fetching once a second confluentinc/librdkafka#2879 (comment)
• Updated Magnus' Add 'fetch.queue.backoff.ms' to the consumer (#2879) patch confluentinc/librdkafka#4275
• Updated Magnus' Add 'fetch.queue.backoff.ms' to the consumer (#2879) patch confluentinc/librdkafka#4284

I've been running a fork of rdkafka incorporating this patched version of librdkafka internally for a couple months. Would you mind if I put up a PR updating rdkafka to that version of librdkafka so I can phase out my fork?

[davidblewett]

@bitemyapp we've recently updated to librdkafka 2.3.0 (in v0.35.0). Can you see if you are able to use this setting now?

[bitemyapp]

@davidblewett I remembered this just yesterday as it happens! I'll take a crack as soon as I am able.