fix!: remove chunk_id property from Chunk class (#3954)

# What does this PR do?

chunk_id in the Chunk class executes actual logic to compute a chunk ID.
This sort of logic should not live in the API spec.

Instead, the providers should be in charge of calling generate_chunk_id,
and pass it to `Chunk`.

this removes the incorrect dependency between Provider impl and API impl

Signed-off-by: Charlie Doern <cdoern@redhat.com>

docs/static/llama-stack-spec.yaml

@@ -9045,6 +9045,10 @@ components:
           description: >-
             The content of the chunk, which can be interleaved text, images, or other
             types.
+        chunk_id:
+          type: string
+          description: >-
+            Unique identifier for the chunk. Must be provided explicitly.
         metadata:
           type: object
           additionalProperties:
@@ -9065,10 +9069,6 @@ components:
           description: >-
             Optional embedding for the chunk. If not provided, it will be computed
             later.
-        stored_chunk_id:
-          type: string
-          description: >-
-            The chunk ID that is stored in the vector database. Used for backend functionality.
         chunk_metadata:
           $ref: '#/components/schemas/ChunkMetadata'
           description: >-
@@ -9077,6 +9077,7 @@ components:
       additionalProperties: false
       required:
         - content
+        - chunk_id
         - metadata
       title: Chunk
       description: >-