Describe the enhancement:
It is currently not possible to import github.com/elastic/beats/cmd.GenRootWithSettings using go modules. This will break (several things):

1. This will retrieve a really old version of the docker-client, which is incompatible
2. The same is true for k8s.io client
3. The github.com/dop251/goja dependencies which are included (vendored) in the github repository, is completely broken. The function RegisterSimpleMaptype() does not exist anymore, and even worse, there are no releases and no branches for this library. The only way to fix this would be to fork the project and revert the changes back to before the deletion of said function.

I therefore propose to fix these dependencies and include a go.mod, to make working with the libbeat library much easier.

I am willing to help with this project and will happily contribute to fixing this.

Describe a specific use case for the enhancement or feature:
Make writing custom beats much easier (when using go modules).