OpenTelemetry Support

[solnic]

This is a small rework of #784 on top of #842 (that got merged).

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Tasks

• Figure out why tests are failing here
• Finalize support for Phoenix
• Finalize support for Oban
• Finalize support for Ecto
• Figure out how parent/children spans should be passed as Transactions when span processor captures only a single root span
• Test it out in a real app

[solnic]

@whatyouhide here we go again - do we want to narrow down the scope of this to ship it in smaller chunks, or do we want an all-in approach? :)

[solnic]

@stephanie-anderson @whatyouhide @sl0thentr0py hey hey, gonna pick it up again. I added a (very high-level) todo. Please chime in if you'd like to reduce the scope here.

[whatyouhide]

I would 100% go with smaller chunks here. We need to PoC this to see how well it scales and all, and I don't think going all in is going to make that easy.

[whatyouhide]

I would also split up PRs that change integration tests because a 2k+/0- diff is not easy to review in too much detail 😉

[solnic]

Closing this in favor of #875