copywrite headers break build tags in Golang

Go [build tags](https://pkg.go.dev/go/build#hdr-Build_Constraints) need to be at the top line of the file to be considered by go compiler.

Right now, running `copyright headers` in go file with build tags would break the tags as the header will be inserted before the build tags.

The expected result is for `copywrite headers` to either:

- offer a way to exclude/include files based on build tags
- detect build tags and insert the header after