Don’t require packages’ dependencies to be declared in the root package.json

| Title | Description
| --------------------|------------
| Version | N/A
| Type | Feature request
| node | N/A
| Operating System | N/A
| Short Description | Don’t require packages’ dependencies to be declared in the root package.json
| Detailed description| It should be possible to have all the benefits of Bolt (except a single source of truth for dependency versions) without requiring that all packages’ dependencies be declared in the root package.json. As it currently stands, when a dependency is removed from a package, developers have to manually garbage collect from the root package’s `dependencies`, by checking for the dependency in all other packages and also checking if any internal tooling depends on the package. The reality is that unused packages accumulate over time, which increases disk usage and how long `bolt install` takes to run, especially in CI pipelines. This would require Bolt to build the list of dependencies otherwise manually provided in the root package.json, and then throw an error when there are mismatched versions between packages. I'd like to keep the root package.json’s `dependencies` section for the internal tools’ dependencies.