contrib/gofiber: add gofiber trace propagation

[mckeown-dd]

This updates gofiber to the earliest version that gave a map for go fiber's request headers. It iterates through those, creates a http.Header object so that the tracer extraction process doesn't have to be modified.

[tylermichael]

I'm running into an issue where APM doesn't connect services because fiber doesn't read the request headers for the distributed span ID. This PR would fix that.

I think this also would have partially addressed this issue: #1222

[ahmed-mez]

Hi @mckeown-dd, thanks for the contribution, can you add a unit test?

[mckeown-dd]

@ahmed-mez. Can you help me figure out why the lint test is failing? Looks like there was already a unit test for propagation, but it didn't really catch the issue. I modified it to check that the trace id is the same as the parent if one is passed.

[ajgajg1134]

@ahmed-mez. Can you help me figure out why the lint test is failing? Looks like there was already a unit test for propagation, but it didn't really catch the issue. I modified it to check that the trace id is the same as the parent if one is passed.

It's your imports list, we enforce a style guide on the grouping and ordering of them as defined here: https://github.com/DataDog/dd-trace-go/wiki/Style-guidelines#imports

It should be a nice quick and easy fix :)

[pr-commenter]

Benchmarks

Found 0 performance improvements and 0 performance regressions! Performance is the same for 6 cases.