Collect licenses of built go binaries

While checking dependency_licenses.json for #2402 (closed), I've noticed that go projects we build do not have their dependencies listed.

I was thinking about this a bit and realised that this should not be a problem of the package. We are building the project and getting the final binary that we ship so we should only care about the license of the final product.

@gitlab-build-team @joshlambert Should we push the license compatibility check back to these projects?

"Offenders":

gitlab-elasticsearch-indexer
gitlab-pages
gitlab-pages
node-exporter
postgres-exporter
prometheus
redis-exporter
registry