new-features.md should be lintable and spell checked

[Joibel]

Pre-requisites

• I have double-checked my configuration
• I have tested with the :latest image tag (i.e. quay.io/argoproj/workflow-controller:latest) and can confirm the issue still exists on :latest. If not, I have explained why, in detail, in my description below.
• I have searched existing issues and could not find a match for this bug
• I'd like to contribute the fix myself (see contributing guide)

What happened? What did you expect to happen?

When generating the new features document for release it fails markdown lint and spelling.

It would be good if it didn't fail, and we knew this up front.

I've not dug into what this would involve exactly, but basically the feature.md documents being produced should be ready for incorporation into new-features.md and we shouldn't ever get a failure at this stage of the process.

I think this involves spell checking the individual feature documents, and post processing the generated features-new.md so it complies with the linter after generation.

These could be two separate PRs.

Version(s)

v4.0-rc1