Document the definition/configuration concept

All the tenanted storage providers use the idea of a _definition_ (an abstract name for some sort of tenanted storage repository) and a _configuration_ (the details required to connect to an actual storage system and locate the right container.

Start by reviewing the existing documentation for the tenanted storage providers and how they describe definitions and configurations. Done means clearly documenting the distinction between a definition—the abstract name of a tenanted repository—and a configuration—the connection and container details for an actual storage system.

Written by the indexing model from the issue text.