feat: allow for provider immutability

being able to update providers means that admins should have the ability to turn this feature off. introduce `immutable` as a field in the Provider class. Defauling to false means all providers can be updated by default, but an admin at runtime can choose to set this to True to disable provider updating

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

llama_stack/distribution/datatypes.py

@@ -151,6 +151,7 @@ class Provider(BaseModel):
     provider_id: str | None
     provider_type: str
     config: dict[str, Any]
+    immutable: bool = False
 
 
 class LoggingConfig(BaseModel):

llama_stack/distribution/providers.py

@@ -147,7 +147,10 @@ class ProviderImpl(Providers):
             if prov_api != api:
                 continue
             for p in providers:
+                # the provider needs to be mutable for us to update its config
                 if p.provider_id == provider_id:
+                    if p.immutable:
+                        raise ValueError(f"Provider {provider_id} is immutable, you can only update mutable providers.")
                     existing_provider = p
                     break
             if existing_provider is not None: