Local Plugin Development and Testing

[arm4b]

Based on bitops-plugins/terraform#7 and #307
At this moment the workflow to develop and test the plugins is time-consuming.

For someone to develop and test the plugin locally they need to push the changes to the git repository first, create a bitops.config.yaml referencing to the git repository and build a docker image based on https://bitovi.github.io/bitops/plugins/#creating-your-own-bitops-image instructions:

bitops:
  plugins:
    terraform:
      source: https://github.com/bitops-plugins/terraform

Instead of that, we could implement file:// handler that would allow using the local plugin directory:

bitops:
  plugins:
    terraform:
      source: file:///path-to-local-bitops-plugin/

This will help with the local development, as well as open opportunity for the automated testing Plugins: Testing / Validation and CI/CD #224 for every plugin, so we can verify that the plugin install really works and verified against the base BitOps on every PR as we change them.