[APM] Display plaintext stacktrace on spans

[AlexanderWert]

Describe the feature:
Currently the stacktraces in spans are only being shown for data coming from the Elastic APM agents, not for OTel-based agents.
Stacktraces reported by OTel agents are in plaintext.
If stacktraces are provided in plain text field (e.g. by OTel agents) they should be displayed in the span flyout.

PR to add a code.stacktrace attribute in semantic conventions: open-telemetry/semantic-conventions#435

A sample document is available in elastic/apm-data#184 description.

[elasticmachine]

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

[SylvainJuge]

I have completed the apm-server/apm-data implementation, which is not yet merged.
A sample span document is available in elastic/apm-data#184 description, which should allow to implement the UI.

[elasticmachine]

Pinging @elastic/obs-ux-infra_services-team (Team:obs-ux-infra_services)

[crespocarlos]

Is the expectation here that the Otel plain text stacktrace is parsed, such that the flyout content can be displayed similar to when Elastic APM agents generate the stack trace?

[SylvainJuge]

No parsing of the stack trace is expected here, at least for now.

The goal is to provide an equivalent UI to what is available in the APM spans, for which we don't have the source code (the example you refer to here probably means source maps have been integrated, which is not available for most APM agents).

Here is what it currently looks like with the Java Elastic APM agent (but the original data is provided parsed and the text rendering is re-implemented in UI to make it look like text).