KAFKA-14597: record-e2e-latency-max only considers consumption latencies but not processing delays

[alanlau28]

Jira: https://issues.apache.org/jira/browse/KAFKA-14597

The record-e2e-latency metric at terminal nodes was computed as currentSystemTimeMs() - record.timestamp(), where currentSystemTimeMs() returns a wall-clock value cached once at the start of processing a record (set by updateProcessorContext before currNode.process() runs). Because this value is captured before the topology executes, processing delays are invisible to it.

The fix reads the wall clock freshly at the terminal site, after child.process() returns. To avoid a clock read per output record the read is done lazily: currentRecordE2ELatencyTimeMs on StreamTask caches the first fresh read and is reused for every subsequent terminal recording within the same input record's processing. updateProcessorContext resets the field to -1 at the start of each record and punctuation, so each input record gets its own reading taken after its processing completes.