tasks: refactor: separate tasks telemetry from workspace builds

[blinkagent]

Related to #973

Background

Currently, the presence of AI-generated tasks in a workspace build is tracked via the workspace_builds.has_ai_task column. This approach couples task telemetry with workspace builds and should be refactored to track tasks as independent entities.

Current Implementation

In coder/coder, the telemetry code at coderd/telemetry/telemetry.go converts workspace builds and includes the has_ai_task field:

func ConvertWorkspaceBuild(build database.WorkspaceBuild) WorkspaceBuild {
	// ...
	if build.HasAITask.Valid {
		wb.HasAITask = ptr.Ref(build.HasAITask.Bool)
	}
	return wb
}

Proposed Changes

1. Remove the has_ai_task field from workspace build telemetry conversion (ConvertWorkspaceBuild)
2. Implement a separate, dedicated telemetry tracking mechanism for tasks
   • Design TBD: Consider tracking task metadata independently rather than as a boolean on workspace builds
   • Should capture task lifecycle events and metrics separately from build lifecycle
3. Once the telemetry change is complete, this will allow removal of the workspace_builds.has_ai_task database column (as tracked in tasks: refactor: remove column workspace_builds.has_ai_task #973)

Dependencies

This work depends on:

• Tasks API: Design and implement tasks data model in database #948
• coder terraform provider: modify coder_ai_task to add app_id and prompt fields #977

Considerations

• The existing SDK usage may remain unchanged for backwards compatibility
• Task telemetry should provide more granular insights than the current boolean flag
• Consider what task-specific metrics would be valuable for telemetry (e.g., task creation, completion, failures, types)
• Removing this telemetry dependency unblocks the database schema cleanup in tasks: refactor: remove column workspace_builds.has_ai_task #973