Related components

Given that components are often released in sets, we should allow users to discover sets of components that have definitions and add these to the components list.

This one is a little abstract as we don't have a concrete way of defining "related". One relationship is Source. Another is "other package format". The scenario that inspired this issue was a set of packages that all go together (e.g., foo-sdk, foo-cli, ...). Unfortunately without some additional context that may be hard to automate.