Support helm plugins properly

[mickmcgrath13]

the bitops config has this section:

    plugins:
      type: object
      properties:
        s3:
          type: object
          properties:
            region:
              type: string
              export_env: HELM_PLUGIN_S3_REGION
            bucket:
              type: string
              export_env: HELM_CHARTS_S3_BUCKET

2 things:

1. ops repo config

the block above suggests that it's configurable at the ops repo level. @PhillypHenning @armab can either of you confirm that ${plugin}.plugins (e.g. helm.plugins) is respected from the core? This would be used when the helm chart s3 bucket's region is different from the default region specified during bitops container startup. ..or at least the HELM_PLUGIN_S3_REGION would. I think the HELM_CHARTS_S3_BUCKET one is superfluous because you include the s3 bucket name when referencing an s3 hosted chart in the Chart.yaml dependencies like:

apiVersion: v2
name: staffing-app wrapper
description: A Helm chart wrapper for the staffing app charts
version: 0.1.0

dependencies:
- name: app-staffing
  version: 0.1.2
  repository: s3://bitovi-operations-staffing-app-helm/charts

2. plugin install

The install script should probably be updated to allow arbitrary plugin installation (should be configured in the plugin.config.yaml