Create a glossary of EF Core terms or otherwise cross-link topics

This will allow docs to link to a simple, short explanation of a term without including that explanation everywhere. It would also be useful if the glossary entities linked to other docs with more details relevant to the term.

For example:
* Tracked/Tracking
* State Manager
* Keyless entity types
* Owned types
* Value conversions
* TPT
* Lazy loading
* Disconnected
* ...