Non discardable api

[eyalkoren]

What does this PR do?

Adds APIs to make spans non-discardable

Checklist

• Added to public API
• Added public API tests
• Added to public API docs
• Added to annotations API
• Added annotations API tests
• Added to annotations API docs
• Added to OTel bridge through a custom attribute
• Added OTel tests
• Added to OTel docs
• Added to CHANGELOG

[ghost]

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• Start Time: 2022-05-24T09:55:57.248+0000

• Duration: 48 min 20 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2904
Skipped	22
Total	2926

💚 Flaky test report

Tests succeeded.

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[eyalkoren]

@SylvainJuge please only take a look at the latest commits adding support for this in the annotations API and not reverting the exposure of the custom attributes as we discussed