Add Debian package metadata and set up CI

.gitlab-ci.yml

debian/README

debian/changelog

debian/compat

debian/control

debian/copyright

debian/docs

debian/gostatsd.default

debian/gostatsd.init

debian/gostatsd.service

debian/rules

debian/source/format

statsd/metrics.go

vendor/github.com/kisielk/cmd/LICENSE

vendor/github.com/kisielk/cmd/README.md

vendor/github.com/kisielk/cmd/cmd.go

vendor/github.com/kisielk/gostatsd/LICENSE

vendor/github.com/kisielk/gostatsd/statsd/aggregator.go

vendor/github.com/kisielk/gostatsd/statsd/console.go

vendor/github.com/kisielk/gostatsd/statsd/doc.go