docs: add autodocs generation for helm values

Summary

Restructure comments section in chart/values.yaml to support helm autodocs, include a README.md.gotpl to re-create README.md using:

docker run -v "$(pwd):/helm-docs" -u $(id -u) jnorwood/helm-docs:v1.5.0 --dry-run -s file -t .gitlab-ci/README.md.gotmpl

Eventually add this to some pre-commit hook.