make cluster sizes configurable in the orchestratord helm chart

[doy-materialize]

Motivation

customers will need to do this, and the defaults we were choosing before don't work with the test suite

currently a draft because it's not quite working yet

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[doy-materialize]

okay, this works after picking names that aren't mz_probe or *cc because those are currently hardcoded to use disk (we should change this, but that will be more effort to fix)

[bobbyiliev]

Looks good!