[v2.9] Migrate from Drone to Github Actions, remove Dapper and add Darwin/arm64 support

[enrichman]

This PR migrates the CI to Drone to GitHub Actions. It also removes dapper.

Secrets were already migrated and tested with https://github.com/rancher/cli/pull/365.

In order to use the golangci/golangci-lint-action the validate script was changed to skip the linting, and a dedicated lint script was added.

As a bonus the arm64 arch was added to the Darwin build (OS_ARCH_ARG[darwin]="amd64 arm64" ), this will fix #329 .