Provide a set of scripts to support offline installs

[don-munro]

Description of the change

This is a POC that should be considered a work in progress. It provides a set of scripts that support customers who cannot pull images directly from docker.io by :

1. For a given Portal version, create a manifest file that identifies the set of images and tags that are required for that version of Portal
2. Use the manifest to pull the required images and optionally upload to a targeted private repo.

Benefits

This is intended to make it easier for customers to pull the correct images for a given portal release. Of note, the image tags for a given version of Portal do not necessarily match the Portal version. As an example, for Portal 5.3.2.1, only dispatcher and portal-data use a 5.3.2.1 tag. All other images use 5.3.2.

Drawbacks

Applicable issues

• fixes #

Additional information

Checklist

• [] Chart version bumped in Chart.yaml according to semver.
• [] Variables are documented in the README.md
• [] Title of the PR starts with chart name (e.g. [charts/gateway])
• [] If the chart contains a values-production.yaml apart from values.yaml, ensure that you implement the changes in both files