[backend:improvement] Add SQL registration Statements in UDF base URL response

[kkampli-singlestore]

We will be moving the creation of UDFs from sdk to the control plane.
These SQL statements will then be called through cellagent to register UDFs against the customer's DB.

Changes:

1. Removed replace_existing argument when calling run_udf_app().
2. sql_statement i.e used to the register the UDF in DB added to udf server response

Sample Response:

{
  "functions": {
    "asdf_test": {
      "args": [],
      "returns": [
        {
          "dtype": "str",
          "nullable": false
        }
      ],
      "function_type": "udf",
      "sql_statement": "CREATE OR REPLACE EXTERNAL FUNCTION asdf_test() RETURNS TEXT NOT NULL AS MANAGED SERVICE \"http://nova-gateway-service.fission.svc.cluster.local:8000/pythonudfs/2ddc0f00-8611-4a79-bb40-928b36cf819f/interactive/\" FORMAT ROWDAT_1;"
    }
  }
}