Enable sane naming of registered objects with defaults (#429)

# What does this PR do? 

This is a follow-up to #425. That PR allows for specifying models in the
registry, but each entry needs to look like:

```yaml
- identifier: ...
  provider_id: ...
  provider_resource_identifier: ...
```

This is headache-inducing.

The current PR makes this situation better by adopting the shape of our
APIs. Namely, we need the user to only specify `model-id`. The rest
should be optional and figured out by the Stack. You can always override
it.

Here's what example `ollama` "full stack" registry looks like (we still
need to kill or simplify shield_type crap):
```yaml
models:
- model_id: Llama3.2-3B-Instruct
- model_id: Llama-Guard-3-1B
shields:
- shield_id: llama_guard
  shield_type: llama_guard
```

## Test Plan

See test plan for #425. Re-ran it.

llama_stack/distribution/routers/routing_tables.py

@@ -32,6 +32,10 @@ async def register_object_with_provider(obj: RoutableObject, p: Any) -> None:
     api = get_impl_api(p)
 
     if obj.provider_id == "remote":
+        # TODO:  this is broken right now because we use the generic
+        # { identifier, provider_id, provider_resource_id } tuple here
+        # but the APIs expect things like ModelInput, ShieldInput, etc.
+
         # if this is just a passthrough, we want to let the remote
         # end actually do the registration with the correct provider
         obj = obj.model_copy(deep=True)
@@ -277,10 +281,10 @@ class MemoryBanksRoutingTable(CommonRoutingTableImpl, MemoryBanks):
         memory_bank_id: str,
         params: BankParams,
         provider_id: Optional[str] = None,
-        provider_memorybank_id: Optional[str] = None,
+        provider_memory_bank_id: Optional[str] = None,
     ) -> MemoryBank:
-        if provider_memorybank_id is None:
-            provider_memorybank_id = memory_bank_id
+        if provider_memory_bank_id is None:
+            provider_memory_bank_id = memory_bank_id
         if provider_id is None:
             # If provider_id not specified, use the only provider if it supports this shield type
             if len(self.impls_by_provider_id) == 1:
@@ -295,7 +299,7 @@ class MemoryBanksRoutingTable(CommonRoutingTableImpl, MemoryBanks):
                 "identifier": memory_bank_id,
                 "type": ResourceType.memory_bank.value,
                 "provider_id": provider_id,
-                "provider_resource_id": provider_memorybank_id,
+                "provider_resource_id": provider_memory_bank_id,
                 **params.model_dump(),
             },
         )