feat!: Migrate Vector DB IDs to Vector Store IDs (breaking change) (#3253)

# What does this PR do?
This change migrates the VectorDB id generation to Vector Stores.

This is a breaking change for **_some users_** that may have application
code using the `vector_db_id` parameter in the request of the VectorDB
protocol instead of the `VectorDB.identifier` in the response.

By default we will now create a Vector Store every time we register a
VectorDB. The caveat with this approach is that this maps the
`vector_db_id` → `vector_store.name`. This is a reasonable tradeoff to
transition users towards OpenAI Vector Stores.

As an added benefit, registering VectorDBs will result in them appearing
in the VectorStores admin UI.

### Why?
This PR makes the `POST` API call to `/v1/vector-dbs` swap the
`vector_db_id` parameter in the **request body** into the VectorStore's
name field and sets the `vector_db_id` to the generated vector store id
(e.g., `vs_038247dd-4bbb-4dbb-a6be-d5ecfd46cfdb`).

That means that users would have to do something like follows in their
application code:

```python
res = client.vector_dbs.register(
    vector_db_id='my-vector-db-id', 
    embedding_model='ollama/all-minilm:l6-v2', 
    embedding_dimension=384,
)
vector_db_id = res.identifier
```

And then the rest of their code would behave, including `VectorIO`'s
insert protocol using `vector_db_id` in the request.

An alternative implementation would be to just delete the `vector_db_id`
parameter in `VectorDB` but the end result would still require users
having to write `vector_db_id = res.identifier` since
`VectorStores.create()` generates the ID for you.

So this approach felt the easiest way to migrate users towards
VectorStores (subsequent PRs will be added to trigger `files.create()`
and `vector_stores.files.create()`).

## Test Plan
Unit tests and integration tests have been added.

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

tests/unit/distribution/routers/test_routing_tables.py

@@ -146,6 +146,20 @@ class VectorDBImpl(Impl):
     async def unregister_vector_db(self, vector_db_id: str):
         return vector_db_id
 
+    async def openai_create_vector_store(self, **kwargs):
+        import time
+        import uuid
+
+        from llama_stack.apis.vector_io.vector_io import VectorStoreFileCounts, VectorStoreObject
+
+        vector_store_id = kwargs.get("provider_vector_db_id") or f"vs_{uuid.uuid4()}"
+        return VectorStoreObject(
+            id=vector_store_id,
+            name=kwargs.get("name", vector_store_id),
+            created_at=int(time.time()),
+            file_counts=VectorStoreFileCounts(completed=0, cancelled=0, failed=0, in_progress=0, total=0),
+        )
+
 
 async def test_models_routing_table(cached_disk_dist_registry):
     table = ModelsRoutingTable({"test_provider": InferenceImpl()}, cached_disk_dist_registry, {})
@@ -247,17 +261,21 @@ async def test_vectordbs_routing_table(cached_disk_dist_registry):
     )
 
     # Register multiple vector databases and verify listing
-    await table.register_vector_db(vector_db_id="test-vectordb", embedding_model="test_provider/test-model")
-    await table.register_vector_db(vector_db_id="test-vectordb-2", embedding_model="test_provider/test-model")
+    vdb1 = await table.register_vector_db(vector_db_id="test-vectordb", embedding_model="test_provider/test-model")
+    vdb2 = await table.register_vector_db(vector_db_id="test-vectordb-2", embedding_model="test_provider/test-model")
     vector_dbs = await table.list_vector_dbs()
 
     assert len(vector_dbs.data) == 2
     vector_db_ids = {v.identifier for v in vector_dbs.data}
-    assert "test-vectordb" in vector_db_ids
-    assert "test-vectordb-2" in vector_db_ids
+    assert vdb1.identifier in vector_db_ids
+    assert vdb2.identifier in vector_db_ids
 
-    await table.unregister_vector_db(vector_db_id="test-vectordb")
-    await table.unregister_vector_db(vector_db_id="test-vectordb-2")
+    # Verify they have UUID-based identifiers
+    assert vdb1.identifier.startswith("vs_")
+    assert vdb2.identifier.startswith("vs_")
+
+    await table.unregister_vector_db(vector_db_id=vdb1.identifier)
+    await table.unregister_vector_db(vector_db_id=vdb2.identifier)
 
     vector_dbs = await table.list_vector_dbs()
     assert len(vector_dbs.data) == 0