Add the (current) transaction name to the error object

[tobiasstadler]

What does this PR do?

Since elastic/apm-server#6539 it is possible to add the transaction name to an error object. I added support for it to the java agent.

Checklist

• This is something else
  • I have updated CHANGELOG.asciidoc

[ghost]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2021-11-08T07:39:24.028+0000

• Duration: 69 min 46 sec

• Commit: befccec

Test stats 🧪

Test	Results
Failed	0
Passed	2493
Skipped	19
Total	2512

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• run benchmark tests : Run the benchmark test.

• run compatibility tests : Run the JDK Compatibility test.

• run integration tests : Run the APM-ITs.

[felixbarny]

Implements elastic/apm#541

[felixbarny]

/test

[felixbarny]

run elasticsearch-ci/docs

[tobiasstadler]

Thank You!