Filter workspace dependencies in the templates (#4599)

This detaches the templates from monorepo's workspace dependencies.

Currently the templates [re-use the monorepo's
dependencies](https://github.com/paritytech/polkadot-sdk-minimal-template/blob/bd8afe66ec566d61f36b0e3d731145741a9e9e19/Cargo.toml#L45-L58),
most of which are not needed.

The simplest approach is to specify versions directly and not use
workspace dependencies in the templates.

Another approach would be to programmatically filter dependencies that
are actually needed - but not sure if it's worth it, given that it would
complicate the synchronization job.

cc @Kianenigma @gupnik