Are Rust workspaces in sub-directories supported?

Hello,

TL;DR how do you tell `release-please` that a Rust workspace is in a sub-directory of the project?

I'm trying to set up a `release-please` flow for my Rust project. My project is set up with a workspace manifest in a sub-directory of the repository (e.g., `rust/Cargo.toml`), and that manifest references several additional directories below it as workspace member crates.

I've tried to use `--path` to specify that my project is in the sub-directory, but I think I must be using it incorrectly because it doesn't seem to work.

Here is an example of what I have tried:

```sh
npx release-please \
release-pr \
--token $TOKEN \
--release-type rust \
--repo-url https://github.com/cdata/noosphere \
--package-name noosphere \
--path rust
```

I've tried a few variations of this, but for whatever reason it can't seem to find my workspace or any of the packages. The best I was able to get out of it was a PR where it thinks it should be versioning my whole project to 0.1.0.

So, I figured I should ask: how do you tell `release-please` that a Rust workspace is in a sub-directory of the project? Is this even supported?

Thank you for your time and consideration.