Fix importing of ECS tracing fields

[jsoriano]

Some groups (base and tracing afaik) contains fields that are not intended to be nested, but belong to the top level.

base was already handled this way, add tracing to the exceptions.

[elasticmachine]

💔 Build Failed

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: 2022-04-01T15:54:50.308+0000

• Duration: 30 min 18 sec

Test stats 🧪

Test	Results
Failed	0
Passed	600
Skipped	0
Total	600

Steps errors

Expand to view the steps failures

Build elastic-package

• Took 4 min 35 sec . View more details here
• Description: make PACKAGE_UNDER_TEST=gcp test-check-packages-parallel

🤖 GitHub comments

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

• /test : Re-trigger the build.

[mtojek]

Error is unrelated, I will merge this PR.