[API Updates] Model / shield / memory-bank routing + agent persistence + support for private headers (#92)

This is yet another of those large PRs (hopefully we will have less and less of them as things mature fast). This one introduces substantial improvements and some simplifications to the stack.

Most important bits:

* Agents reference implementation now has support for session / turn persistence. The default implementation uses sqlite but there's also support for using Redis.

* We have re-architected the structure of the Stack APIs to allow for more flexible routing. The motivating use cases are:
  - routing model A to ollama and model B to a remote provider like Together
  - routing shield A to local impl while shield B to a remote provider like Bedrock
  - routing a vector memory bank to Weaviate while routing a keyvalue memory bank to Redis

* Support for provider specific parameters to be passed from the clients. A client can pass data using `x_llamastack_provider_data` parameter which can be type-checked and provided to the Adapter implementations.

docs/openapi_generator/generate.py

@@ -18,16 +18,16 @@ import yaml
 
 from llama_models import schema_utils
 
+from .pyopenapi.options import Options
+from .pyopenapi.specification import Info, Server
+from .pyopenapi.utility import Specification
+
 # We do some monkey-patching to ensure our definitions only use the minimal
 # (json_schema_type, webmethod) definitions from the llama_models package. For
 # generation though, we need the full definitions and implementations from the
 #  (json-strong-typing) package.
 
-from strong_typing.schema import json_schema_type
-
-from .pyopenapi.options import Options
-from .pyopenapi.specification import Info, Server
-from .pyopenapi.utility import Specification
+from .strong_typing.schema import json_schema_type
 
 schema_utils.json_schema_type = json_schema_type
 
@@ -43,9 +43,13 @@ from llama_stack.apis.post_training import *  # noqa: F403
 from llama_stack.apis.reward_scoring import *  # noqa: F403
 from llama_stack.apis.synthetic_data_generation import *  # noqa: F403
 from llama_stack.apis.safety import *  # noqa: F403
+from llama_stack.apis.models import *  # noqa: F403
+from llama_stack.apis.memory_banks import *  # noqa: F403
+from llama_stack.apis.shields import *  # noqa: F403
 
 
 class LlamaStack(
+    MemoryBanks,
     Inference,
     BatchInference,
     Agents,
@@ -57,6 +61,8 @@ class LlamaStack(
     PostTraining,
     Memory,
     Evaluations,
+    Models,
+    Shields,
 ):
     pass