KAFKA-6581: Fix the ConsumerGroupCommand indefinite execution if one of the partition is unavailable.

[SahilAggarwal]

• Checks if partition available before calling consumer.position
• Adds timeout on consumer.position() call.

Committer Checklist (excluded from commit message)

• [ ] Verify design and implementation
• [ ] Verify test coverage and CI build status
• [ ] Verify documentation (including upgrade notes)