feat: combine ProviderSpec datatypes (#3378)

# What does this PR do?

currently `RemoteProviderSpec` has an `AdapterSpec` embedded in it.
Remove `AdapterSpec`, and put its leftover fields into
`RemoteProviderSpec`.

Additionally, many of the fields were duplicated between
`InlineProviderSpec` and `RemoteProviderSpec`. Move these to
`ProviderSpec` so they are shared.

Fixup the distro codegen to use `RemoteProviderSpec` directly rather
than `remote_provider_spec` which took an AdapterSpec and returned a
full provider spec

## Test Plan

existing distro tests should pass.

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

llama_stack/distributions/starter/starter.py

@@ -78,12 +78,12 @@ def get_remote_inference_providers() -> list[Provider]:
     remote_providers = [
         provider
         for provider in available_providers()
-        if isinstance(provider, RemoteProviderSpec) and provider.adapter.adapter_type in ENABLED_INFERENCE_PROVIDERS
+        if isinstance(provider, RemoteProviderSpec) and provider.adapter_type in ENABLED_INFERENCE_PROVIDERS
     ]
 
     inference_providers = []
     for provider_spec in remote_providers:
-        provider_type = provider_spec.adapter.adapter_type
+        provider_type = provider_spec.adapter_type
 
         if provider_type in INFERENCE_PROVIDER_IDS:
             provider_id = INFERENCE_PROVIDER_IDS[provider_type]