Allow using dependecies/overrides with relative path

[varditn]

Expected Behaviour

Usage of a relative path as the location for the chart in prereqCharts, additionalValues or dependencies will use the local copy of the chart.

Actual Behaviour

There is no option to use relative path for charts location, only git repo or chart repo.

Example

prereqCharts:
  - cert-manager:
      packaged: false
      pathToChart: ./helm/cert-manager
      overrideValueFiles:
        - values.yaml