Add entries to catalog for non-Pressbooks published material

[SteelWagstaff]

As a network manager, I want to to be able to list items in my catalog that were published by the institution using tools other than Pressbooks so that I can showcase all of the works of my organization/press.

To support this, Pressbooks should allow network managers to enter the required metadata directly as a 'catalog' entry and display this alongside of Pressbooks-published books.

We'll need to work out the UX/UI design for this and specify the required & optional input values. They should broadly match the information displayed on the catalog 'book card' or filtered by the filter tools. If we build this we should probably build an additional filter that allows people to filter by Pressbooks native & non-Pressbooks or something like that.