Add Go module file

[nezorflame]

In order for others to use the only currently supported vendor solution aka Go modules, this project needs a go.mod file.

This would also help with confusion some people have over the import name (DataDog vs datadog) - since the module file will contain the package name, it'll be the only proper import path after the module file gets merged.

Which one it should have is probably up for discussion (or as the author decides).

[nezorflame]

@Viq111 thanks!

[Viq111]

Sorry for the delay!
We were looking at #91 which is a release blocker.
As soon as it's merged (hopefully soon, just need to be able to consistently reproduce in CI tests), I'll cut a new release. I would recommend waiting for that PR to be merged first