Allow to specify multiple value files

[milosgajdos]

Is your feature request related to a problem? Please describe.
Helm charts often contain multiple values files (usually to override default values with per-environment values) e.g.

• values.yaml
• values.test.yaml

Unfortunately, currently this action only provides support for a single values file not giving any choice to the usr to override the defaults with test values or whatnot

Describe the solution you'd like
I'd like to provide a list of value files so the action does something like this helm lint -f values.yaml -f values.foo.yaml .

Describe alternatives you've considered
There is no other alternative provided by helm I'm afraid -- at least not to my knowledge

Additional context

[imalik8088]

Perhaps an alternative, because I needed also to update my deps before doing the helm template command:

jobs:
  helm-check:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@master
    - name: Install Helm
      uses: azure/setup-helm@v1
      with:
        version: v3.5.1
    - name: helm-check-operator
      run: |
        cd ./operator
        helm dep up
        helm lint . --debug
        helm template -f values.yaml -f other-values.yaml . --debug

[igabaydulin]

There is CHART_VALUES environment variable which indeed allows to specify only one file with values. Probably we can make it work with multiple values files eg. separating it with ;:

env:
        CHART_LOCATION: ./helm-check-action-sample
        CHART_VALUES: ./helm-check-action-sample/values/test1.yaml;./helm-check-action-sample/values/test2.yaml

We just need to update entrypoint.sh and make it to parse CHART_VALUES variable. Currently I don't have time for this implementation, but you're welcome to create a pull request with this change