GraphQL JSON type filter options

Along the lines of #882
Wanted to keep the discussions separate so I opened a separate issue, but the question remains the same. What filter options should be provide for JSON type.

E.g. Postgres has pretty good json support: https://www.postgresql.org/docs/current/functions-json.html
So we can consider adding filtering options like json-s with key "a".

首先阅读 issue #882 以及此处链接的 PostgreSQL JSON 函数文档。文档中没有指定实现文件、入口点或测试；首先需要决定 GraphQL API 应支持哪些 JSON 过滤选项，并定义如何验证完成情况。

由索引模型根据 Issue 内容生成。