Support for multiple tool calls

[christianliebel]

It is possible that multiple tool calls will come out here: https://github.com/thinktecture-labs/ng-forms-companion/blob/main/projects/smart-form-filler/src/lib/backends/open-ai-tools-backend.ts

In general, it's best to provide all choices. You'll also need the callId, and you should execute and respond with the ID and value, including the history.