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 #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
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
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    • .feature: Signifying a new feature.
    • .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.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[vbhavsar]

Wireshark capture of FetchRequest V11 packet. It includes the new rack_id field serialized.

[vbhavsar]

Default values derived from https://github.com/a0x8o/kafka/blob/master/clients/src/main/resources/common/message/FetchRequest.json