Support multiple create mutation for self-referencing relationships.

[severussundar]

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.