feat: Add method to get event fields inside a Hook

[erezrokah]

Hi 👋 Thank you for this great module 🚀

Opening for feedback as an attempt to fix #493, #587, also referenced from https://github.com/open-telemetry/opentelemetry-go-contrib/pull/5918/files#diff-a9b82897838da6b8eed398e03c9590621e6c2336ff576b3a49fb684ff8bba2a1R110

This is not the cleanest approach, but could be better from using reflection. It doesn't expose the internal buffer representation format so if it ever changes GetFields can be modified.

Feedback very much welcomed

[erezrokah]

Thanks for the quick review @ccoVeille, followed up with the suggestions and added more tests. Also please see the comment about the tradeoff of using JSON Decode

[ccoVeille]

Thanks for applying the changes, here are a few more feedbacks

[ccoVeille]

LGTM 🤞

[chkp-omris]

@ccoVeille @erezrokah I'd also be very happy to have this feature merged, I happened to find this PR looking for a solution.
May I suggest that the implementation simply returns the internal buffer buf to avoid forcing JSON decoding on the user?

[erezrokah]

@ccoVeille @erezrokah I'd also be very happy to have this feature merged, I happened to find this PR looking for a solution.
May I suggest that the implementation simply returns the internal buffer buf to avoid forcing JSON decoding on the user?

I following #637 (comment) as not to expose the internal buf. If we expose buf and then later there's a need to change the internal representation of the event to something else it will be harder to do

[mark-ten9]

It would be great to merge this if possible so that we don't have to use reflection to work around this.

[nduong-ol]

Hello, it has been a while. Would it be possible to merge this PR?