support consumer groups in tail config

[isaacd9]

Support consumer groups in tail.

Adds an argument to topicctl tail to support a consumer group --group-id. If set, this disables the partitions command is passed down to the reader.

I also updated repl with this.

I'm happy to write a test for this but would love some instruction on the preferred way to do so in this repo.

[hhahn-tw]

Hello - thanks for the contribution. While the command line form seems to work as expected, I'm having trouble with the repl form. When running eg. tail my-topic--group-id my-repl-group, it seems not to consume at all: it doesn't output any messages despite producing to it (via topicctl tester) and the group id is not reported by neither topicctl get groups nor kafka-consumer-groups.sh.

Without the --group-id flag, it works as expected (messages are output on the console as they are consumed).

Can you clarify what may be wrong?

Separately - can you update the help text for the repl form to include the --group-id flag?