Migrate to GH actions

[jkroepke]

Hi,

i recently read

It would be great if anyone could enahnce our CI workflow to cover cygwin (if it's possible).

• Use cygpath for HELM_BIN #287 (comment)

and thought I can re-design the CI workflow in general in form as a proposal.

The new CI based on Github Action. It covers all tasks from Circle CI +

• helm plugin install on MacOS and Windows (3 variants)
• integration tests against real kubernetes
• Linting the shell script install-binary.sh with shellcheck, shfmt and checkbashisms. Covered by https://github.com/luizm/action-sh-checker

To gain a preview of the flow, take a look here: https://github.com/jkroepke/helm-diff/actions/runs/1673641310

Most parts of the CI workflow are copied from https://github.com/jkroepke/helm-secrets

As mention in the tests, the installation on cygwin is broken.

[mumoshu]

cc/ @databus23 Are you happy with enabling/using GitHub Actions on this repo? (I am 😃 But I wanted to confirm

[databus23]

Sure. Lets do it.

[jkroepke]

To initially setup github action

• this needs to be merged first
  OR
• the PR author needs to be a collaborator.
  OR
• In worst, the PR author needs to be a collaborator and this branch needs to be a local branch.

I would suggest @databus23 or @mumoshu create a branch (not a fork), merge my branch into it and create a new pull request.

I guess, Github does not allow external contributers to create new workflows.

[mumoshu]

LGTM. I'm merging this anyway. Let's address any issues(if any) after the first run of this on our master branch.
Thanks a lot for your contribution @jkroepke!