Fix missing otel transaction attributes

[SylvainJuge]

What does this PR do?

Transactions created through the OTel bridge were missing the otel attributes map when sending data to apm-server.

Checklist

• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix

[github-actions]

/test

[apmmachine]

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Build stats

• Start Time: 2022-06-01T11:50:11.798+0000

• Duration: 48 min 46 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2904
Skipped	22
Total	2926

💚 Flaky test report

Tests succeeded.

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