Add support for sub-resources

We need to be able to support recursive child-containers which are resolved dynamically during routing. Do we want explicit support for this, or simply rely on users creating sub-routers and dynamically creating LDAP containers on the fly?

Here's some additional use cases taken from OPENDJSDK-70: multi-tenant and deep hierarchical layout of resources in LDAP:

1. multi-tenant support using simple naming (e.g. tenant = "example")
   • URI pattern: /{tenant}/users/{id}
   • DN pattern: uid={id},ou=people,dc={tenant},dc=com
2. multi-tenant support using regex naming (e.g. tenant = "example.com")
   • URI pattern: /{tenant}/users/{id}
   • Regex pattern: ([^.]+)\.([^.]+)
   • DN pattern: uid={id},ou=people,dc=$1,dc=$2
3. deep hierarchy:

   dc=com,dc=example
   |
   +---ou=org1
   |   +---uid=user1A
   |   +---uid=user1B
   |   +---...
   |
   +---ou=org2
   |   +---uid=user2A
   |   +---uid=user2B
   |   +---...
   |
   +---...
   

Where you want a single HTTP end-point /users for all users regardless of their organizational unit. The assumption is that the associated JSON resources would contain a field indicating the OU to which the resource belongs. This would allow create (POST) requests to work since the parent DN cannot be determined without this information.