Previously there were two methods:
* `_find_coordinator_id()`
* `_find_many_coordinator_ids()`

But they do basically the same thing internally. And we need the plural
two places, but the singular only one place.

So merge them, and change the function signature to take a list of
`group_ids` and return a dict of `group_id: coordinator_id`s.

As a result of this, the `describe_groups()` command should scale better
because the `_find_coordinator_ids()` command issues all the requests
async, instead of sequentially blocking as the `described_groups()` used
to do.

Small cleanup leftover from https://github.com/dpkp/kafka-python/pull/2035

* Add consumergroup related errors
* Add DeleteGroups to protocol.admin
* Implement delete_groups feature on KafkaAdminClient

Currently there's no way to pass timeout to check_version if called from admin.

Adding namedtuples for DescribeConsumerGroup response; Adding Serialization of MemberData and MemberAssignment for the response

Co-authored-by: Apurva Telang <atelang@paypal.com>
Co-authored-by: Jeff Widman <jeff@jeffwidman.com>

In KAFKA-8962 the `AdminClient.describe_topics()` call was changed from
using the controller to using the `least_loaded_node()`:
https://github.com/apache/kafka/commit/317089663cc7ff4fdfcba6ee434f455e8ae13acd#diff-6869b8fccf6b098cbcb0676e8ceb26a7R1540

As a result, no metadata request/response processing needs to happen
through the controller, so it's safe to remove the custom
error-checking. Besides, I don't think this error-checking even added
any value because AFAIK no metadata response would return a
`NotControllerError` because the recipient broker wouldn't realize the
metadata request was intended for only the controller.

Originally our admin client was implemented using the least-loaded-node,
then later updated to the controller. So updating it back to
least-loaded node is a simple case of reverting the associated commits.

This reverts commit 7195f0369c7dbe25aea2c3fed78d2b4f772d775b.

This reverts commit 6e2978edee9a06e9dbe60afcac226b27b83cbc74.

This reverts commit f92889af79db08ef26d89cb18bd48c7dd5080010.

Closes #1994