支持自定义搜索SQL查询

[mnixry]

Please make sure of the following things

• [X] I have read the documentation.
• [X] I'm sure there are no duplicate issues or discussions.
• [X] I'm sure this feature is not implemented.
• [X] I'm sure it's a reasonable and popular requirement.

Description of the feature / 需求描述

在MySQL和PostgreSQL中，存在多种插件/扩展程序来优化数据库的全文搜索能力，例如PGroonga，Mroonga，zhparser 等。

在大量AList用户存在CJK文本搜索的需求，而MySQL/PGSQL对CJK搜索支持较为薄弱的情况下，使用自定义的搜索引擎/扩展就显得尤为重要。通常来讲，使用这些搜索扩展需要对SQL查询进行不同程度的改动，而目前硬编码SQL查询的代码写法暂不支持这种需求。

Suggested solution / 实现思路

https://github.com/alist-org/alist/blob/83c22693306f36853d6c6c2b50f567d9b58cb834/internal/db/searchnode.go#L57-L74

从配置文件中读取SQL查询模板以代替使用硬编码的SQL查询来进行

Additional context / 附件

个人不是很熟悉AList项目的组织架构，如果有意见以及建议请多指教。

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