Add support for EKS clusters and fix helm v3 home issue

[rvichery]

As discussed in #22, the kubeconfig for an EKS cluster relies on having the aws CLI available. This PR adds the aws-cli dependency and configure the PYTHONPATH so the aws command can find its modules.

Passing opts was not necessary as github exec is by default passing all environment variables to the child process: https://github.com/actions/toolkit/blob/master/packages/exec/src/interfaces.ts#L9

I also addressed an issue with helm3 introduced by adding the --home-path. I switched to using environment variables as suggested on Helm guides: https://helm.sh/docs/faq/#xdg-base-directory-support.

[apooniajjn]

@rvichery excellent work. This allowed me to use this action to deploy chart easily on EKS cluster.

[colinjfw]

This looks great, thanks for your contribution @rvichery. I'll merge this into master and release it hopefully in the next few days.

Leaving it on master for a bit tends to catch bugs before pushing it to v1 with users that run with master selected.

[benjick]

How do I use this? I'm using EKS

My action looks like this:

- name: 'Deploy'
  uses: 'deliverybot/helm@master'
  with:
    release: 'ui'
    namespace: 'default'
    chart: '.helm'
    token: '${{ github.token }}'
    helm: helm3
  env:
    KUBECONFIG_FILE: ${{ secrets.KUBECONFIG }}
    AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
    AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}

but I'm getting this error: Error: UPGRADE FAILED: "ui" has no deployed releases

Works fine locally