Add option for non-clickable breadcrumbs

[rkwilliamson]

Request: Option to add breadcrumbs to documentation pages as non-clickable text, rather than links to the top page in a docs section.

We don't have "overview" root pages in all sections of our documentation, which means that the user experience isn't great when using breadcrumbs to navigate.

For example, in the following nav structure, there's an overview page for the main category, as a complex concept, but not for the sub-category because it's simple enough that we don't need one.

Using the example structure below, with clickable breadcrumbs, a user reading an individual item page might click the Sub-category breadcrumb, potentially expecting an overview page, but would actually land on the page for Item A.

We're considering adding overview pages but they aren't always necessary - creating them would be unnecessary work and ongoing maintenance. A good workaround would be a non-clickable option for breadcrumbs to help users see the steps they've taken to find the current page and navigate within the docs without the issue of landing on unrelated pages.

Main category
- Overview (root page of main category group)
-- Sub-category (does not need a root page)
---- Item A
---- Item B
---- Item C