* linting with new golangci-lint version
* update go to 1.18
* bump versions in drone.yml
* use new runtime/debug package for version info
* remove Commit build flag from goreleaser
* remove mock commit + version from build script
* go fmt
* add dummy version env flag to test container
* install git in golang container for testing
* only set versionString if Version is defined
* update drone to create latest manifest
* add .dockerignore file
* use buildx for multi-arch builds
see https://docs.docker.com/buildx/working-with-buildx/
* don't use RUN commands in Dockerfile
this was breaking multi-arch builds