[APM] Show stack trace on errors when only available as plain text

[AlexanderWert]

Summary

Closes #124204

Shows plaintext stacktrace when it's only available as a value in error.stack_trace (which is mostly the case with OTel and mobile agents).

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

[elasticmachine]

Pinging @elastic/apm-ui (Team:APM)

[apmmachine]

🤖 GitHub comments

Expand to view the GitHub comments

Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[sorenlouv]

lgtm. Just one question

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 0555bf1

Failed CI Steps

• APM Cypress Tests #3

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
apm	1408	1409	+1

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
apm	3.6MB	3.6MB	+415.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	13	15	+2
securitySolution	416	420	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	14	16	+2
securitySolution	497	501	+4
total			+6

History

• 💚 Build #125810 succeeded a410997

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream