We should redirect old individual package docs to the main Ocean docs

We have had unified docs for quite a while now (https://github.com/dwavesystems/dwave-ocean-sdk/pull/40 was merged in 2019). We should add redirects from the legacy individual doc pages to the Ocean docs. For instance [dwave-system's docs](https://docs.ocean.dwavesys.com/projects/system/en/latest/) are very out of date.

This could/should coincide with update the individual repo links. I think most of them now link to the unified docs, but perhaps not all. Likewise there are some lingering issues (e.g. https://github.com/dwavesystems/dwave-ocean-sdk/issues/150 that should be resolved).