feat(remote.Client): Add current context to Fetch and FetchV2

[hbiarge]

Summary

Add a field in the Config type to provide the internal http.Client the remote.Client is going to use.

No breaking changes. Same default behaviour as before.

Allow instrumenting remote http calls providing a wrapped http.Client.

Pass the current Context to Fetch and FetchV2 to enable distributed tracing.

Fixes #28

Checklist

• [ x] Does your PR title have the correct title format?
• Does your PR have a breaking change?: No
• Does your PR have a breaking change?: Yes

[hbiarge]

Well, I'm not an expert in Go, but, after investigating a little bit my problem, I can instrument the underlying RoundTripper used by the http.Client.
So the issue is now that we need the current context when we call Fetch and FetchV2 to be able to retrieve the current parent span from the current context and let the distributed tracing system to make it's magic.

[bgiori]

Hey @hbiarge thanks so much for submitting this PR. Unfortunately I don't want to break the existing API on the client for Fetch and FetchV2, but your approach is correct.

Can you add FetchV2WithContext instead of update the existing function? Then FetchV2 can just call FetchV2WithContext.

[hbiarge]

Sure, it makes totally sense.
I'm on holiday this week, but I will update the PR when I find some time.
Thank you so much!

[hbiarge]

Ready for review @bgiori...

[github-actions]

🎉 This issue has been resolved in version 1.6.0 🎉

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