[Known Issue] Add support for PostgreSQL Stored-Procedure

[abhishekkumams]

DAB currently supports Executing Stored-procedure for GraphQL/REST for MSSQL, We need to extend this support to PGSQL as well.

doc: https://github.com/Azure/data-api-builder/blob/main/docs/internals/StoredProcedureDesignDoc.md
mssql PR: #979

[Aniruddh25]

Moving to Mar2023 since it needs to add support for executing Functions as well for PG.