Update datadog exporter error tagging

[ericmustin]

Description

Fixes #244(#244). I think this is ready for review, pretty straightforward, when span status is not ok we iterate over events and look for exception info.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Updated Unit Tests

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[ericmustin]

cc @majorgreys @alertedsnake @codeboten reviews welcome! cheers

[majorgreys]

Is the existing test sufficient to test the new event exception extraction?

[ericmustin]

@majorgreys I think so? our existing test raises an error with start_span, which ensures span.record_exception gets called and adds an exception event. See here. I updated the test to ensure all 3 relevant tags for datadog errors are getting extracted.

[majorgreys]

@ericmustin Thanks! Should a test be added for the fallback? Is there any scenario where this fallback is necessary?

[ericmustin]

@majorgreys yea im not sure, i think let's just remove the old fallback approach, in practice we should never need it now, will update

[alertedsnake]

This looks great, thanks @ericmustin! I'm glad you got a chance to work on it before I could :)

[lzchen]

@majorgreys
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