add helm/helm and other helm subproject maintainers to maintainers.cncf.io

I've been going through the oldest issues looking to see why they're not resolved. Some of them could be resolved by open PRs that could have been but were not merged for quite some time. It seems like we need more maintainers.

One value individuals and companies get from maintaining upstream projects (besides the obvious stable code and feedback to ensure their business needs are met) is community recognition. This recognition provides value to the contributor and their employer and just feels good. Part of that is being recognized as a maintainer by the CNCF, and being able to take part in discussions on the cncf-helm-maintainers list.

Currently, only the nine Helm Org maintainers are listed as Helm maintainers on the official CNCF spreadsheet.

Some of our team is also involved in the Flux project. We have seen where Weaveworks has implemented a strategy where they collect all the names in all the MAINTAINERS files from all the repos for submission to the CNCF. If we did something similar, I think we could get more maintainers, shorten the PR backlog, and that would lead to more contributors and a healthier community.