Ignore lookup_coordinator result in commit_offsets_async

[asafflesch]

Fixes an issue where if commit_offsets_async has to lookup the coordinator before actually sending the offset_commit_request, the request will fail with the following error:

Error processing callback
Traceback (most recent call last):
  File "/home/runner/pipeline.runfiles/kafka_python_git/kafka/future.py", line 79, in _call_backs
    f(value)
TypeError: _do_commit_offsets_async() takes from 2 to 3 positional arguments but 4 were given

This is because the current logic directly adds the invocation of _do_commit_offsets_async as a callback to the invocation of lookup_coordinator, but _do_commit_offsets_async has no use for that value, and has no parameter to receive it, resulting in the above error. This PR just passes a wrapper lambda as the actual callback to the invocation of lookup_coordinator.

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This change is 

[jeffwidman]

This makes sense to me.

@dpkp / @tvoinarovskyi your thoughts? If we are going to take this, it'd be nice to get it in before the next release.

@Faqa can you rebase/squash to a single commit?

[tvoinarovskyi]

Can't this just be something like:
future.add_callback(lambda r: self._do_commit_offsets_async(offsets, callback))
More readable... Or does it not work?

[tvoinarovskyi]

Kind of find the partial part a bit hard to read.

[dpkp]

Thanks for the catch + bugfix!