Unified/Contextual Search Extension

Currently organisation/group and package search are distinct, and there is no resource search (although you can use package search to do this).

Rather than just have package search (at /dataset) only return packages, it might be useful to have it also search for organisations and resources. Although you can search for these via the package search, the UI shows you the package that contains the resource, or the package that belongs to the organisation.

Would be nice to have an extension that searched datasets, organisations and resource (metadata) and displayed this differently on the search results. This way I could search for an organisation from a single search box, or search and see that my search for 'health' returned X datasets, but also here are organisations with 'health' in the name. And these 10 resources also have health in the filename even though it isn't mentioned in the description.

I guess my user stories are:

As a user
I want a single unified place to search
So that I don't see different behaviour in different places

As a user
I want a single unified place to search
So that I don't have to navigate to another page to find organisations

As a user
I want search to also find resources
So that I discover things based on original/uploaded filename

As a developer
I want an interface I can implement
So that I can mark my own objects as searchable (i.e. showcase, pages).

No files, tests, or entry points are named. Start by reviewing the requested user stories and define the scope for one unified search across datasets, organisations, and resources, including the extensible searchable-object interface; done means these result types are discoverable and distinguishable in one place.

Written by the indexing model from the issue text.