Problem/Motivation
Some plugin types might have a LOT of plugin definitions. Menu links is one exampe but block_content could also provide a lot of potential custom blocks,
which would be too much for the derivative system.
Proposed resolution
One possiblity would be a StoragePluginManagerInterface which adds addDefinition()/updateDefinition()/removeDefinition().
The implementations would have to store this data inside a new database table and retrieve data from there.