Add helm chart

This MR brings the helm chart from https://www.gitlab.com/CodethinkLabs/lorry/lorry2-e2e (with minor codestyle changes).

Part of #70 (closed)

CI for packaging publishes a new helm chart for every:

• merge request
  • with tag {LATEST TAG OR 0.0.0}-dev.{COMMIT SHA}
• commit to the default branch
  • with tag {LATEST TAG OR 0.0.0}-main.{DATE}.{COMMIT SHA}
• release
  • with tag equal to the release tag without the v prefix (the prefix is removed in order to comply w/ semver). This means that:
    • lorry2 helm chart version is always equal to lorry2 release version (just without the v prefix)