(core) Add telemetry for AI Assistant

Summary: Also fixes a few bugs with some telemetry events not being recorded.

Test Plan: Manual.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3960

app/common/AssistancePrompts.ts

@@ -35,6 +35,7 @@ export type AssistanceContext = FormulaAssistanceContext;
  * A request for assistance.
  */
 export interface AssistanceRequest {
+  conversationId: string;
   context: AssistanceContext;
   state?: AssistanceState;
   text: string;