A long time ago, `api_version` supported strings. That has been
deprecated for years in favor of tuples. Time to remove support for the
strings.

The docs for `api_version_auto_timeout_ms` mention setting
`api_version='auto'` but that value has been deprecated for years in
favor of `api_version=None`.

Updating the docs for now, and will remove support for `'auto'` in next
major version bump.

If the cluster metadata object has no info about the topic, then issue a blocking metadata call to fetch it.

Use `futures` to parallelize calls to `_send_request_to_node()`

This allows queries that need to go to multiple brokers to be run in parallel.

Now that the old zookeeper consumer has been completely deprecated/removed, these are no longer the "new consumer configs" but rather simply the "consumer configs"

1. Remove unused variable: `partitions_for_topic`
2. No need to cast to list as `sorted()` already returns a list
3. Using `enumerate()` is cleaner than `range(len())` and handles assigning
`member`