support export trace info to app for external usage

[yjqg6666]

Feature

Export txId & spanId to application. Disabled by default.

Usage

If my application need to save/notify some system the txId/spanId, i could

1. import com.navercorp.pinpoint:pinpoint-application-interaction:2.0.2 as dependency.
2. fetch the txId/spanId

TraceInfo traceInfo = TraceInfoHolder.getTraceInfo();
String txId = TraceInfoHolder.getTransactionId();
long spanId = TraceInfoHolder.getSpanId();

Scene

In kafka lower version client/broker which do not support KAFKA header, now we could get the txId & spanId and put these info into message body, then the consumer can get the trace info and log. Now i can also save txId & my biz id(order id/user id etc) to db together.

Before this PR, we could only get the txId/spanId from slf4j.MDC in a hacky way.

[codecov-commenter]

Codecov Report

Merging #6801 into master will decrease coverage by 0.04%.
The diff coverage is 1.08%.

@@            Coverage Diff             @@
##           master    #6801      +/-   ##
==========================================
- Coverage   39.23%   39.18%   -0.05%     
==========================================
  Files        3195     3199       +4     
  Lines       94770    94862      +92     
  Branches    11844    11861      +17     
==========================================
- Hits        37179    37175       -4     
- Misses      54612    54706      +94     
- Partials     2979     2981       +2     

Impacted Files	Coverage Δ
...int/interaction/trace/export/DefaultTraceInfo.java	0.00% <0.00%> (ø)
...nteraction/trace/export/TraceInfoExportHelper.java	0.00% <0.00%> (ø)
...oint/interaction/trace/export/TraceInfoHolder.java	0.00% <0.00%> (ø)
...rp/pinpoint/interaction/util/ClassLoaderUtils.java	0.00% <0.00%> (ø)
...p/pinpoint/bootstrap/classloader/ProfilerLibs.java	100.00% <ø> (ø)
...tstrap/agentdir/AgentDirBaseClassPathResolver.java	53.21% <ø> (ø)
...quest/ServletRequestListenerInterceptorHelper.java	57.53% <14.28%> (-4.59%)	⬇️
...p/pinpoint/rpc/client/WriteFailFutureListener.java	56.25% <0.00%> (-18.75%)	⬇️
...rc/main/java/com/navercorp/pinpoint/test/Item.java	66.66% <0.00%> (-3.34%)	⬇️
...cluster/zookeeper/ZookeeperClusterDataManager.java	52.90% <0.00%> (-1.94%)	⬇️
... and 7 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d773da8...8822907. Read the comment docs.

[emeroad]

@yjqg6666
I have a question
If I remove pinpiont-agent in an application using export api, does it work normally?

[yjqg6666]

@yjqg6666
I have a question
If I remove pinpiont-agent in an application using export api, does it work normally?

It would not affect the application, just no write only read, null TraceInfo/TransactionId would be return.

[yjqg6666]

TraceInfo traceInfo = TraceInfoHolder.getTraceInfo();
String txId = TraceInfoHolder.getTransactionId();
long spanId = TraceInfoHolder.getSpanId();

Have tested and checked that the above three variables would always be null if no pinpoint in javaagent or the request is not sampled. The package com.navercorp.pinpoint:pinpoint-application-interaction must have no extra dependency introduced.
@emeroad