docs: add documentation on how to use custom run yaml in docker (#3949)

as title

test plan:

```yaml
# custom-ollama-run.yaml
version: 2
image_name: starter
external_providers_dir: /.llama/providers.d
apis:
- inference
- vector_io
- files
- safety
- tool_runtime
- agents

providers:
  inference:
  # Single Ollama provider for all models
  - provider_id: ollama
    provider_type: remote::ollama
    config:
      url: ${env.OLLAMA_URL:=http://localhost:11434}

  vector_io:
  - provider_id: faiss
    provider_type: inline::faiss
    config:
      persistence:
        namespace: vector_io::faiss
        backend: kv_default

  files:
  - provider_id: meta-reference-files
    provider_type: inline::localfs
    config:
      storage_dir: /.llama/files
      metadata_store:
        table_name: files_metadata
        backend: sql_default

  safety:
  - provider_id: llama-guard
    provider_type: inline::llama-guard
    config:
      excluded_categories: []

  tool_runtime:
  - provider_id: rag-runtime
    provider_type: inline::rag-runtime

  agents:
  - provider_id: meta-reference
    provider_type: inline::meta-reference
    config:
      persistence:
        agent_state:
          namespace: agents
          backend: kv_default
        responses:
          table_name: responses
          backend: sql_default
          max_write_queue_size: 10000
          num_writers: 4

storage:
  backends:
    kv_default:
      type: kv_sqlite
      db_path: /.llama/kvstore.db
    sql_default:
      type: sql_sqlite
      db_path: /.llama/sql_store.db
  stores:
    metadata:
      namespace: registry
      backend: kv_default
    inference:
      table_name: inference_store
      backend: sql_default
      max_write_queue_size: 10000
      num_writers: 4
    conversations:
      table_name: openai_conversations
      backend: sql_default

registered_resources:
  models:
  # All models use the same 'ollama' provider
  - model_id: llama3.2-vision:latest
    provider_id: ollama
    provider_model_id: llama3.2-vision:latest
    model_type: llm
  - model_id: llama3.2:3b
    provider_id: ollama
    provider_model_id: llama3.2:3b
    model_type: llm
  # Embedding models
  - model_id: nomic-embed-text-v2-moe
    provider_id: ollama
    provider_model_id: toshk0/nomic-embed-text-v2-moe:Q6_K
    model_type: embedding
    metadata:
      embedding_dimension: 768
  shields: []
  vector_dbs: []
  datasets: []
  scoring_fns: []
  benchmarks: []
  tool_groups: []

server:
  port: 8321

telemetry:
  enabled: true

vector_stores:
  default_provider_id: faiss
  default_embedding_model:
    provider_id: ollama
    model_id: toshk0/nomic-embed-text-v2-moe:Q6_K
```

```bash
docker run
     -it
     --pull always
     -p $LLAMA_STACK_PORT:$LLAMA_STACK_PORT
     -v ~/.llama:/root/.llama
     -v $CUSTOM_RUN_CONFIG:/app/custom-run.yaml
     -e RUN_CONFIG_PATH=/app/custom-run.yaml
     -e OLLAMA_URL=http://host.docker.internal:11434/
     llamastack/distribution-starter:0.3.0
     --port $LLAMA_STACK_PORT
```

src/llama_stack/distributions/template.py

@@ -424,6 +424,7 @@ class DistributionTemplate(BaseModel):
                 providers_table=providers_table,
                 run_config_env_vars=self.run_config_env_vars,
                 default_models=default_models,
+                run_configs=list(self.run_configs.keys()),
             )
         return ""