This commits adds `LoadChartMetadataFromArchive` and
`LoadChartMetadataFromDir` helpers to the internal `helm` package
to be able to make observations to the Helm metadata file without
loading the chart in full.
The helpers are compatible with charts of the v1 format (with a
separate `requirements.yaml` file), and an additional
`LoadChartMetadata` helper is available to automatically call the
right `LoadChartMetadataFrom*` version by looking at the file
description of the given path.
Signed-off-by: Hidde Beydals <hello@hidde.co>