Move goals pages to direction page structure

Created by: jyavorska

The goals pages are being updated to follow the direction page format at https://about.sourcegraph.com/handbook/product/product_management/direction_template, so this PR reorganizes them to be under the /direction heirarchy, along with the rest of the company direction. This PR is mainly just fixing links associated with the move.

This has the added benefit of moving some content that was split between being in product and engineering handbooks to a shared space.