Support multiple create mutation for self-referencing relationships.

PR https://github.com/Azure/data-api-builder/pull/2138 adds support for querying relationships that reference the same entity (self-join tables).

Extend multiple create functionality to support relationships that reference itself.

Some things to consider are:
- Accurate determination of referencing/referenced entity. Though, referenced and referencing entity are both the same, we need to be able to identify whether **top level item** (or) **related item** should be created first.
- The current data structure maintains the relationship metadata at the entity level. PR https://github.com/Azure/data-api-builder/pull/2138 introduces changes to maintain the relationship metadata at the granularity level of relationship. This new data structure should be used during query generation and rest of the mutation flows.

まず PR #2138 を確認して、自己参照リレーションのメタデータと複数作成 mutation のフローを理解します。クエリ生成と残りの mutation パスを追跡し、自己参照リレーションにおいてトップレベルのアイテムと関連アイテムが正しい順序で作成されることを確認します。

索引モデルが issue の本文から書いたものです。