Remaining issues with release-please

There are still a few remaining issues with our release-please (RP) setup

1. **Infinite loop of releases** - When RP searches through our commits, it still includes commits that have already been released leading to duplicated releases with ever growing changelogs
2. **Cargo workspaces** - RP will bump the versions in the Cargo.toml of each package (graph-proxy, sessionspaces) but it won't update the Cargo.lock file in /backend. This leads to a combination of manual and automatic version bumps. The [Cargo-workspace](https://github.com/googleapis/release-please/blob/main/docs/manifest-releaser.md#cargo-workspace) plugin seems like the correct way to fix this, but unfortunately it does not seem to work with our current structure of subfolders /backend and /frontend.
3. **Helm chart versions are not bumped by RP** - at least I couldn't find a way to do this. This means that for some releases (graph-proxy, sessionspaces, dashboard) we need to make an additional version bump commit on the release PR to do this. Not the end of the world, but a little annoying.