Add support for rack id in the consumer

[vbhavsar]

Changes

• Introduce a new rack_id parameter on AIOKafkaConsumer and store it on the instance.
• Propagate rack_id (alongside new session metadata fields session_id, session_epoch and forgotten_topics_data) into the internal Fetcher.
• Revise fetch-request version logic:
  • For kafka 2.4.0+ clients, bump to FetchRequest V11 and include the consumer's rack_id in the payload
  • Fall back to the existing protocal branches (V7 and V4) for older API versions

Fixes aio-libs#1016

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
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    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
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