Change OTel quickstart to use log4j2 instead of logback

[aabmass]

Log4j2's JsonTemplateLayout supports most of the Cloud Logging special JSON keys directly through the GcpLayout event template. I still needed to map the OTel MDC keys for trace correlation, but am planning to contribute this upstream.

One outstanding issue is converting the trace_flags hex value to a boolean, but it doesn't break Cloud Console if logging.googleapis.com/trace_sampled key is unset/false. See apache/logging-log4j2#2482.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• examples/instrumentation-quickstart/src/main/resources/log4j2.xml:21, tag opentelemetry_instrumentation_setup_logging

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[aabmass]

This is a different region tag than the docs currently use

opentelemetry-operations-java/examples/instrumentation-quickstart/src/main/resources/logback.xml

Line 19 in 97a8f20

<!-- [START opentelemetry_instrumentation_logbackxml] -->

So I can update the docs before removing the logback.xml files

[dashpole]

if this returns false, will that just be a no-op? (do we actually need to comment out this config?)

[aabmass]

Ah good point. I was trying to prevent collector log spam, but it looks like the log spam is actually coming from the remove operator:

2024-04-18T14:52:50.317Z error helper/transformer.go:98 Failed to process entry {"kind": "receiver", "name": "filelog", "data_type": "logs", "operator_id": "remove6", "operator_type": "remove", "error": "remove: field does not exist: body['logging.googleapis.com/trace_sampled']", "action": "send", "entry": {"observed_timestamp":"2024-04-18T14:52:50.317546122Z","timestamp":"2024-04-18T14:52:50.214Z","body":{"_exception":{"stackTrace":""},"_logger":"com.example.demo.SingleController","_thread":"reactor-http-epoll-20","logging.googleapis.com/insertId":"2037","logging.googleapis.com/labels":{"span_id":"5aeb502bb6ef209f","trace_flags":"01","trace_id":"5643ea6d8d99b1b30a6fbab66b1a3ddd"},"logging.googleapis.com/sourceLocation":{"function":"com.example.demo.SingleController.handleSingle"},"message":"Going to sleep for 172"},"attributes":{"log.file.name":"app.log"},"severity_text":"INFO","span_id":"WutQK7bvIJ8=","trace_id":"VkPqbY2ZsbMKb7q2axo93Q==","severity":9,"scope_name":""}}

I'll just let it be for now and reset this file