cli: consumer-offset set always says consumer for group kinds #4459

Split from #4450.

Problem

iggy consumer-offset set always says "consumer", also when -k consumer-group or -k external-group is used. The text is hard-coded in explain, the error context and the success message (core/cli/src/commands/binary_consumer_offsets/set_consumer_offset.rs:60, :71, :77).

consumer-offset get already gets this right with get_consumer_info (core/cli/src/commands/binary_consumer_offsets/get_consumer_offset.rs:52).

Proposal

Use the same wording as get_consumer_info in all three places in set_consumer_offset.rs, either by moving it to a shared helper or by adding the same method to SetConsumerOffsetCmd.

Acceptance

• consumer-offset set -k consumer-group ... prints "consumer group with ID: ...", and -k external-group prints "external group with ID: ...".
• -k consumer (the default) prints the same text as today.
• core/integration/tests/cli/consumer_offset/test_consumer_offset_set_command.rs covers the consumer and external group kinds and passes.