Improve Helm installer security, add Helm chart linting
Three main components:
- Moving the Helm installer inside the repo, and enforcing signature checks as well as checksum verification. This covers both the CI job and node operator local installs.
- Added a Helm chart linting step, and moved all linting into a locally runnable script (for easy local checking before pushing to remote -
make lint
) - Created a Dockerfile for building the CI image for this repository.