Release v20.68.0

Summary

A read model is loaded by the command's key, and only Chronicle resolved one.

Added

• A command declares the key its read models are loaded by, in an application without Chronicle: a property marked with the data annotations [Key], or an ICanProvideKeyForCommand composing it. The key may be a Guid, int, long, string, or a ConceptAs<T> wrapping one of those (#2303)
• ICanResolveKeyForCommand, for keying commands your own way across an application. It is asked before the rule Arc ships, whichever order the two are discovered in (#2303)
• ARCCHR0008 reports a command marking its key with the data annotations [Key] in an application that uses Chronicle, where it silently resolves nothing (#2303)

Fixed

• Injecting a read model into a command no longer fails as a validation error in an application that has Entity Framework Core or MongoDB but no Chronicle (#2303)