Add kamon http4s

[vaslabs]

Moves kamon-http4s here.

Noteable events:

• I've followed the same approach as kamon cats io and adapted the same structure as the kamon-http4s project with 2 separate modules.
• Publishing will be identical to the kamon-http4s project, not sure if you want to namespace it

- We have left a common configuration because we identified common code, but haven't changed anything from the original source. My suggestion is we release as is and then we can refactor the common code to avoid investigation of what changed for any weird regressions .
We have added the Y-partial-unification flag to the common compilation settings of 2.12, it seemed easier, we can move to http4s only if deemed necessary
We followed the kamon-akka as a template for the setup, but we have not changed the original kamon-http4s code, only the sbt setup

Please let us know if we missed anything, I've tested +test, +publishLocal in the kamon-http4s project

Credits and special thanks

This PR is co-authored with @irodotos7 and our time was funded by @vaslabs-ltd

[vaslabs]

there's a flaky test, potentially needs some investigation so it doesn't become a problem for the whole release process

Also the packaging is problematic, this will need a bit more work

[vaslabs]

I've addressed the flakiness as best as I could and changed the approach on structuring the modules + publishing, ready to be reviewed!