Add dana agent provider stub

- Register inline::dana provider in agents registry
- Add stub implementation with get_provider_impl function
- Add DanaAgentConfig with sample_run_config
- Include dana provider in starter, starter-gpu, and ci-tests distributions
- All agent methods currently raise NotImplementedError until implementation

src/llama_stack/distributions/ci-tests/run.yaml

@@ -171,6 +171,8 @@ providers:
           backend: sql_default
           max_write_queue_size: 10000
           num_writers: 4
+  - provider_id: dana
+    provider_type: inline::dana
   post_training:
   - provider_id: torchtune-cpu
     provider_type: inline::torchtune-cpu