Found docs updates needed from ADK python release v1.15.1 to v1.16.0

This issue outlines the necessary documentation updates based on the changes in the ADK Python repository from release v1.15.1 to v1.16.0.

**Compare Link:** https://github.com/google/adk-python/compare/v1.15.1...v1.16.0

Here are the recommended changes:

1. **LLM Context Compaction**
- **File:** `docs/sessions/index.md` and `docs/agents/llm-agents.md`
- **Change:** Add documentation for the new LLM context compaction feature. This is a significant new feature that helps manage the size of the conversation history.
- **Details:**
- In `docs/sessions/index.md`, add a new section introducing the concept of context compaction and its importance for managing long-running conversations.
- In `docs/agents/llm-agents.md`, add a detailed section explaining how to configure and use the context compaction feature with `LlmAgent`. Include code examples.

2. **Pause and Resume Invocation**
- **File:** `docs/runtime/index.md` and `docs/tools/function-tools.md`
- **Change:** Add a new section to the runtime documentation explaining the explicit pause and resume feature, especially for long-running tools.
- **Details:**
- In `docs/runtime/index.md`, under the "Important Runtime Behaviors" section, add a new subsection explaining how an invocation can be paused by a `LongRunningFunctionTool` and resumed later.
- In `docs/tools/function-tools.md`, expand the section on `LongRunningFunctionTool` to provide a more detailed explanation of the pause and resume mechanism.

3. **Gemma Model Support**
- **File:** `docs/agents/models.md`
- **Change:** Add documentation for the newly supported Gemma model.
- **Details:**
- Add a new section for the Gemma model, similar to the existing sections for other models.
- Include instructions on how to use it with the Gemini API and provide a code example.

4. **BigQuery `execute_sql` `dry_run`**
- **File:** `docs/tools/built-in-tools.md`
- **Change:** Update the documentation for the BigQuery `execute_sql` tool to include the new `dry_run` parameter.
- **Details:**
- In the description of the `execute_sql` tool, mention the `dry_run` parameter and explain its purpose.

5. **BigQuery `analyze_contribution` Tool**
- **File:** `docs/tools/built-in-tools.md`
- **Change:** Add the new `analyze_contribution` tool to the list of BigQuery tools.
- **Details:**
- In the BigQuery toolset section, add a new bullet point for the `analyze_contribution` tool with a brief description of its functionality.

6. **Spanner Template and Parameterized SQL**
- **File:** `docs/tools/built-in-tools.md`
- **Change:** Add documentation for the new support for customizable template SQL and parameterized SQL in the Spanner toolset.
- **Details:**
- Add a new section explaining how to use template SQL and parameterized SQL with the Spanner toolset, with code examples based on `contributing/samples/spanner/agent.py`.

7. **OAuth2 Client Credentials Grant Type**
- **File:** `docs/tools/authentication.md`
- **Change:** Add a new section to the authentication documentation to cover the OAuth2 Client Credentials grant type.
- **Details:**
- Add a new subsection under the OAuth2 section explaining the Client Credentials grant type, using the code from the `oauth2_client_credentials` sample as an example.

8. **`ReflectRetryToolPlugin`**
- **File:** `docs/plugins/index.md`
- **Change:** Add a new page to the plugins section to document the `ReflectRetryToolPlugin`.
- **Details:**
- Create a new markdown file for the `ReflectRetryToolPlugin` and link it from the main plugins page.
- The new page should explain the purpose of the plugin, its features, and how to use it, based on the docstring in the plugin's source code.

9. **`VertexAiSearchTool` with Multiple Tools**
- **File:** `docs/tools/built-in-tools.md`
- **Change:** Update the documentation to reflect that `VertexAiSearchTool` and `google_search` can now be used with other tools in the same agent.
- **Details:**
- Remove the limitation notice that states only one built-in tool can be used at a time.
- Add a new section that explains how to use multiple built-in tools together, with a code example.

10. **New Evaluation Metrics**
- **File:** `docs/evaluate/index.md`
- **Change:** Add documentation for the new `HallucinationsV1` and "Rubric based tool use" evaluation metrics.
- **Details:**
- Add new sections describing these new metrics and how to use them.

11. **`adk web` Custom Logo**
- **File:** `docs/get-started/quickstart.md`
- **Change:** Add documentation for the new `--logo-text` and `--logo-image-url` options for the `adk web` command.
- **Details:**
- In the section that explains how to use `adk web`, add a subsection for the new custom logo options with a brief explanation and example.

12. **OpenAPI `$defs` Support**
- **File:** `docs/tools/openapi-tools.md`
- **Change:** Update the OpenAPI documentation to mention the new support for `$defs`.
- **Details:**
- In the "How it Works" section, add a bullet point that mentions the support for resolving `$defs` in OpenAPI schemas.