Instrument `http4s`

[ptrdom]

Closes https://github.com/ScalaConsultants/mesmer/issues/667

[ptrdom]

TODO:

• [ ] Create an e2e test for http4s.
• [ ] Add tests for error cases. I have investigated doing that for each metric, but ran into an annoying issue where apparently testRunner.clearAllExportedData() does not actually clear exported metrics, so having multiple tests for single metric seemed impossible to do.

[lgajowy]

TODO for future reference:

• an example project could be useful that shows the metrics