feat: introduce APIs for retrieving chat completion requests (#2145)

# What does this PR do?
This PR introduces APIs to retrieve past chat completion requests, which
will be used in the LS UI.

Our current `Telemetry` is ill-suited for this purpose as it's untyped
so we'd need to filter by obscure attribute names, making it brittle.

Since these APIs are 'provided by stack' and don't need to be
implemented by inference providers, we introduce a new InferenceProvider
class, containing the existing inference protocol, which is implemented
by inference providers.

The APIs are OpenAI-compliant, with an additional `input_messages`
field.


## Test Plan
This PR just adds the API and marks them provided_by_stack. S
tart stack server -> doesn't crash

llama_stack/distribution/resolver.py

@@ -13,7 +13,7 @@ from llama_stack.apis.datasetio import DatasetIO
 from llama_stack.apis.datasets import Datasets
 from llama_stack.apis.eval import Eval
 from llama_stack.apis.files import Files
-from llama_stack.apis.inference import Inference
+from llama_stack.apis.inference import Inference, InferenceProvider
 from llama_stack.apis.inspect import Inspect
 from llama_stack.apis.models import Models
 from llama_stack.apis.post_training import PostTraining
@@ -83,6 +83,13 @@ def api_protocol_map() -> dict[Api, Any]:
     }
 
 
+def api_protocol_map_for_compliance_check() -> dict[Api, Any]:
+    return {
+        **api_protocol_map(),
+        Api.inference: InferenceProvider,
+    }
+
+
 def additional_protocols_map() -> dict[Api, Any]:
     return {
         Api.inference: (ModelsProtocolPrivate, Models, Api.models),
@@ -302,9 +309,6 @@ async def instantiate_provider(
     inner_impls: dict[str, Any],
     dist_registry: DistributionRegistry,
 ):
-    protocols = api_protocol_map()
-    additional_protocols = additional_protocols_map()
-
     provider_spec = provider.spec
     if not hasattr(provider_spec, "module"):
         raise AttributeError(f"ProviderSpec of type {type(provider_spec)} does not have a 'module' attribute")
@@ -342,6 +346,8 @@ async def instantiate_provider(
     impl.__provider_spec__ = provider_spec
     impl.__provider_config__ = config
 
+    protocols = api_protocol_map_for_compliance_check()
+    additional_protocols = additional_protocols_map()
     # TODO: check compliance for special tool groups
     # the impl should be for Api.tool_runtime, the name should be the special tool group, the protocol should be the special tool group protocol
     check_protocol_compliance(impl, protocols[provider_spec.api])