[Automatic Import] Add positive FTR functional tests

[bhapas]

The failure scenarios for different Auto import routes are being tested but the functional tests that test the positive behaviour need to be added. A mock / stubbed LLM server is required for this #199089 can solve this.

Once this server is available in security solution , we need to add positive functional api tests.

[elasticmachine]

Pinging @elastic/security-scalability (Team:Security-Scalability)