Use GitHub Workflows for CI tests and goreleaser based releases

[displague]

This PR is doing a few things, happy to break it out if needed:

• update packngo to latest
• add a custom UserAgent to packngo API calls with the docker-machine-driver-packet release tag
• add linting checks as a github workflow
• add goreleaser as a github workflow task
• add release badges to the README.md
• ignore .vscode/ in git

[displague]

tested with:

• golangci-lint run .
• goimports -w .
• go test -v ./...
• goreleaser check
• goreleaser build
• act -P ubuntu-latest=nektos/act-environments-ubuntu:18.04

Ultimately verified by merging and tagging this into the master of my fork, where the workflow succeeded in producing a release and running all of the tests.

[displague]

While testing that the binary worked, I found that the User-Agent was not being transmitted. Not the fault of this branch, but of equinixmetal-archive/packngo#188.

This may help anyone else looking to debug this plugin:

go build
PACKNGO_DEBUG=1 PATH=`pwd`:$PATH docker-machine \
  --debug create -d packet \
  --packet-api-key=$PACKET_TOKEN \
  --packet-project-id=$PACKET_PROJECT \
  foo