Implement an optional breadcrumb override

Problem/Motivation

In earlier versions, G2 overrode the breadcrumbs systems, placing full page g2_entry node views below the main glossary page.

Over time, this proved to lead to UX issues, especially when the glossary was not the main component of a site, which is the most frequent case.

Steps to reproduce

n.a.

Proposed resolution

In D8+ this override has been removed, and this feature is about introducing it as an optional feature, under configuration control, so that glossary-centered sites can use it, but others do not have to.

Remaining tasks

Design and develop.

User interface changes

Breadcrumbs now follow the default Drupal logic until this feature is implemented to possibly override that logic.

API changes

None.

Data model changes

None.