feat(es9): add Elasticsearch 9 indexer and retriever components

[kaijchen]

What type of PR is this?

feat

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• This PR title match the format: <type>(optional scope): <description>
• The description of this PR title is user-oriented and clear enough for others to understand.
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feat(es9): 实现 Elasticsearch 9 indexer 和 retriever 组件

(Optional) More detailed description for this PR(en: English/zh: Chinese).

en:
This PR implements the Indexer and Retriever components for Elasticsearch 9.x (ES9), enabling integration with the latest Elasticsearch version.

Key changes:

1. Indexer (components/indexer/es9):

   • Implemented core Indexer logic and adapted for go-elasticsearch/v9.
   • Supports batch indexing and custom field mapping.
   • Full documentation (README) and examples included.
   • Verified with github.com/elastic/go-elasticsearch/v9.

2. Retriever (components/retriever/es9):

   • Implemented Retriever interface with support for multiple search modes:
     • Approximate (KNN, Hybrid, RRF)
     • Dense Vector Similarity (Script Score)
     • Exact Match
     • Raw String (DSL)
     • Sparse Vector Query
   • Updated API usage to match ES9 client changes (e.g., ScriptScore.Query type change, Similarity enum).
   • Comprehensive tests and examples.

3. Verification:

   • All unit tests passed.
   • Verified against a local Elasticsearch 9 Docker instance with TLS enabled.
   • Verified backward compatibility of design references (consistent with ES7/ES8 patterns).

zh:
此 PR 实现了 Elasticsearch 9.x (ES9) 的 Indexer 和 Retriever 组件，支持与最新版本的 Elasticsearch 集成。

主要变更：

1. Indexer (components/indexer/es9):

   • 适配了 go-elasticsearch/v9 客户端。
   • 支持批量索引和自定义字段映射。
   • 包含完整的文档和示例代码。

2. Retriever (components/retriever/es9):

   • 实现了 Retriever 接口，支持多种搜索模式：
     • 近似搜索 (KNN, 混合搜索, RRF)
     • 稠密向量相似度 (Script Score)
     • 精确匹配
     • 原始字符串查询 (DSL)
     • 稀疏向量查询
   • 适配了 ES9 客户端的 API 变更（如 ScriptScore.Query 类型和 Similarity 枚举）。
   • 包含完整的测试和示例。

3. 验证:

   • 所有单元测试通过。
   • 在开启 TLS 的本地 Elasticsearch 9 环境中验证了所有示例。

(Optional) Which issue(s) this PR fixes:

(optional) The PR that updates user documentation:

[N3kox]

lgtm