Improvement: Log warning if there is no output when fetching offsets

[tomverelst]

There is currently no output if there are no consumer groups.

Expected

Log a warning

How to reproduce

Fetch offsets from a topic without consumer groups.

#/usr/bin/env bash

set -eo pipefail

API_KEY=...
API_SECRET=...
CLUSTER=...
TOPICS=.

cargo build --release

target/release/bridge-cli fetch-source \
-b $CLUSTER \
-o "security.protocol=SASL_SSL" \
-o "sasl.mechanism=PLAIN" \
-o "sasl.username=$API_KEY" \
-o "sasl.password=$API_SECRET" \
-t TOPICS

[wserr]

@tomverelst is this a good error, or too much/too little information? I have added this for now, can be changed.

[2025-10-15T15:53:23Z WARN  bridge_core::commands::fetch_source_offsets::sources::client] No offsets were found on topics-partition combos {"__consumer_offsets": [0, 1, 2, 3, 4, 5, 6, 7, 8, 9
, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49], "orders-3": [0], "orders-2":
 [0], "orders-1": [0]}