What does this PR do?

This makes sure that the "standard and most common" way of compiling and deploying Go apps is working when using dd-trace-go.

Add a new test app called setup-smoke-test which sets up dd-trace-go and all its products on a basic net/http server.
The Dockerfile is a parameterized multi-stage Dockerfile with docker args and multiple targets allowing us to cover the main setup of our users we do not want to ever break:

• golang docker image being used, with a matrix of:
  • go version
  • distribution: alpine or debian.
  • with or without go mod vendor
  • with or without CGO
  • alpine with gcc and the C librray headers
• deployment docker image with a matrix of:
  • bare alpine (musl-based distrib)
  • bare docker (glibc-based distrib)
  • alpine with libc6-compat
  • amazonlinux
  • docker's scratch image

Motivation

Avoid compilation and/or deployment breaking changes. This makes sure that the "standard and most common" way of compiling and deploying Go apps is working when using dd-trace-go.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!