Modify Repository find* methods to include navigational properties

[bajtos]

Modify Repository find* method signatures to include navigational properties in the description of the return type

• Add a new generic parameter Relations to CRUD-related Repository interfaces and implementations.
• Modify the signature find and findById to return T & Relations instead of T. If this requires too many explicit casts, then consider using T & Partial<Relations> instead, assuming it improves the situation.

See the spike #2592 for more details, especially the changes made in packages/repository/src/repositories/repository.ts and packages/repository/src/repositories/legacy-juggler-bridge.ts.

Acceptance criteria

• Modify Repository interfaces and classes as described above
• Update API documentation
• Update lb4 model to start emitting {ModelName}Relations interfaces
• Update lb4 repository to include {ModelName}Relations in the generic parameters of DefaultCrudRepository we are inheriting from