helm: Do not render empty fields (subPath, args, env & envFrom)

[adberger]

What this PR does

Many fields in the mimir-distributed helm chart are templated, even if no values are specified. This PR should fix these.

Checklist

• [ ] Tests updated.
• [ ] Documentation added.
• [x] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [ ] about-versioning.md updated with experimental features.

[CLAassistant]

All committers have signed the CLA.

[adberger]

@dimitarvdimitrov I'm not sure how to proceed from here.
I've ran make build-helm-tests and pushed a new commit, but since upstream was already updated there is a conflict. What's the best approach?

[dimitarvdimitrov]

we don't have strict git instructions. But what I'd do is

1. squash your 4 commits into 1 (git rebase -i HEAD~4 and then mark all of them as f or s)
2. make sure your local upstream:main ref is up to date
3. rebase onto upstream:main
4. force-push to adberger:main

[adberger]

@dimitarvdimitrov I tried my best, can you rerun the tests?

[adberger]

Apologies, I gave it another try.