feat: more logs when the input data is wrong somehow

[vrischmann]

This PR improves the logs to help track down where a label might be wrong.

Before:

2024-01-29T16:14:59.659+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping
2024-01-29T16:14:59.659+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping
2024-01-29T16:14:59.660+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping
2024-01-29T16:14:59.660+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping
2024-01-29T16:14:59.660+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping
2024-01-29T16:14:59.660+0100	INFO	vimebu@v1.1.0/vimebu.go:171	label value must not be empty, skipping

After:

2024-01-29T16:13:10.496+0100	INFO	vimebu/vimebu.go:171	metric: "kafka_broker_connect", label name: "host", label value must not be empty, skipping
2024-01-29T16:13:10.497+0100	INFO	vimebu/vimebu.go:171	metric: "kafka_broker_write_wait", label name: "host", label value must not be empty, skipping
2024-01-29T16:13:10.497+0100	INFO	vimebu/vimebu.go:171	metric: "kafka_broker_bytes_written", label name: "host", label value must not be empty, skipping
2024-01-29T16:13:10.497+0100	INFO	vimebu/vimebu.go:171	metric: "kafka_broker_write_latencies", label name: "host", label value must not be empty, skipping

[wazazaby]

LGTM, thank you :)