feat(metrics): track consumer records lag

[tinaselenge]

No description provided.

[tinaselenge]

@dnwe would you mind reviewing the PR please? I fixed the cla failure and lint errors it was reporting.

[hindessm]

I think it makes sense to pull the lagMetric != nil check up so we avoid doing working out for nothing. That is:

Suggested change

	if len(b.RecordsSet) > 0 {
	logEndOffset := *b.LastRecordsBatchOffset - 1
	partitionLag := logEndOffset - b.RecordsSet[len(b.RecordsSet)-1].RecordBatch.LastOffset()
	if lagMetric != nil {
	lagMetric.Update(partitionLag)
	}
	}
	if lagMetric != nil && len(b.RecordsSet) > 0 {
	logEndOffset := *b.LastRecordsBatchOffset - 1
	partitionLag := logEndOffset - b.RecordsSet[len(b.RecordsSet)-1].RecordBatch.LastOffset()
	lagMetric.Update(partitionLag)
	}

[github-actions]

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