Migrate chart documentation to helm-docs

[ccremer]

https://github.com/norwoodj/helm-docs addresses an issue long present in helm charts:

There is often documentation and comments in values.yaml, and there is documentation in README.md.
There isn't a clear source of truth, as with manually maintained README it can get out-of-date pretty soon.

helm-docs follows the approach where the README is entirely generated from Chart metadata and values.yaml. however, it requires that comments in the yaml file follow a certain style in order to be properly parsed.

This issue aims to migrate the charts to make them "helm-docs-compatible" i.e. generate nicer READMEs.