Finder filter restriction in content item
Finder filter restriction in content item

As Finder Frontend becomes more generic, we want to be able to specify
how we restrict the default filter. This commit adds it to the content
item when it is published.

We also move the `document_type` into the `filter` as
`filter_document_type`.

alphagov/contacts-admin,alphagov/contacts-admin,alphagov/contacts-admin