KSTREAMS-8781: Add back rack.aware.assignment.tags config

[gabriellefu]

Adds broker-side plumbing for rack.aware.assignment.tags to support rack-aware standby task assignment in Kafka Streams (new consumer group protocol). This does not include the assignor logic change — only the config propagation and client-side validation.

Changes:

• Define group.streams.rack.aware.assignment.tags as a broker-level config (GroupCoordinatorConfig) with a per-group override streams.rack.aware.assignment.tags (GroupConfig)
• Plumb the config through streamsGroupAssignmentConfigs() so config changes automatically trigger group epoch bumps and reassignment
• Add RackAwareAssignmentTags field to the StreamsGroupHeartbeatResponse RPC schema and populate it in the heartbeat response
• On the client side, compare the broker's required tags against the client's client.tag.* keys and log a WARN for any missing tags
• Add unit tests for config parsing, assignment config plumbing, response building, and client-side warning logic