[memory refactor][3/n] Introduce RAGToolRuntime as a specialized sub-protocol (#832)

See https://github.com/meta-llama/llama-stack/issues/827 for the broader
design.

Third part:
- we need to make `tool_runtime.rag_tool.query_context()` and
`tool_runtime.rag_tool.insert_documents()` methods work smoothly with
complete type safety. To that end, we introduce a sub-resource path
`tool-runtime/rag-tool/` and make changes to the resolver to make things
work.
- the PR updates the agents implementation to directly call these typed
APIs for memory accesses rather than going through the complex, untyped
"invoke_tool" API. the code looks much nicer and simpler (expectedly.)
- there are a number of hacks in the server resolver implementation
still, we will live with some and fix some

Note that we must make sure the client SDKs are able to handle this
subresource complexity also. Stainless has support for subresources, so
this should be possible but beware.

## Test Plan

Our RAG test is sad (doesn't actually test for actual RAG output) but I
verified that the implementation works. I will work on fixing the RAG
test afterwards.

```bash
pytest -s -v tests/agents/test_agents.py -k "rag and together" --safety-shield=meta-llama/Llama-Guard-3-8B
```

llama_stack/providers/inline/tool_runtime/memory/config.py

@@ -4,87 +4,8 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from enum import Enum
-from typing import Annotated, List, Literal, Union
-
-from pydantic import BaseModel, Field
-
-
-class _MemoryBankConfigCommon(BaseModel):
-    bank_id: str
-
-
-class VectorMemoryBankConfig(_MemoryBankConfigCommon):
-    type: Literal["vector"] = "vector"
-
-
-class KeyValueMemoryBankConfig(_MemoryBankConfigCommon):
-    type: Literal["keyvalue"] = "keyvalue"
-    keys: List[str]  # what keys to focus on
-
-
-class KeywordMemoryBankConfig(_MemoryBankConfigCommon):
-    type: Literal["keyword"] = "keyword"
-
-
-class GraphMemoryBankConfig(_MemoryBankConfigCommon):
-    type: Literal["graph"] = "graph"
-    entities: List[str]  # what entities to focus on
-
-
-MemoryBankConfig = Annotated[
-    Union[
-        VectorMemoryBankConfig,
-        KeyValueMemoryBankConfig,
-        KeywordMemoryBankConfig,
-        GraphMemoryBankConfig,
-    ],
-    Field(discriminator="type"),
-]
-
-
-class MemoryQueryGenerator(Enum):
-    default = "default"
-    llm = "llm"
-    custom = "custom"
-
-
-class DefaultMemoryQueryGeneratorConfig(BaseModel):
-    type: Literal[MemoryQueryGenerator.default.value] = (
-        MemoryQueryGenerator.default.value
-    )
-    sep: str = " "
-
-
-class LLMMemoryQueryGeneratorConfig(BaseModel):
-    type: Literal[MemoryQueryGenerator.llm.value] = MemoryQueryGenerator.llm.value
-    model: str
-    template: str
-
-
-class CustomMemoryQueryGeneratorConfig(BaseModel):
-    type: Literal[MemoryQueryGenerator.custom.value] = MemoryQueryGenerator.custom.value
-
-
-MemoryQueryGeneratorConfig = Annotated[
-    Union[
-        DefaultMemoryQueryGeneratorConfig,
-        LLMMemoryQueryGeneratorConfig,
-        CustomMemoryQueryGeneratorConfig,
-    ],
-    Field(discriminator="type"),
-]
-
-
-class MemoryToolConfig(BaseModel):
-    memory_bank_configs: List[MemoryBankConfig] = Field(default_factory=list)
+from pydantic import BaseModel
 
 
 class MemoryToolRuntimeConfig(BaseModel):
-    # This config defines how a query is generated using the messages
-    # for memory bank retrieval.
-    query_generator_config: MemoryQueryGeneratorConfig = Field(
-        default=DefaultMemoryQueryGeneratorConfig()
-    )
-    max_tokens_in_context: int = 4096
-    max_chunks: int = 5
+    pass