Instead of creating tasks with a specialized call to `CreateWorkspace`
on the frontend, we instead lift this to the backend and allow the
frontend to simply call `CreateAITask`.
Add an endpoint to fetch AI task prompts for multiple workspace builds
at the same time. A prompt is the value of the "AI Prompt" workspace
build parameter. On main, the only way our API allows fetching workspace
build parameters is by using the `/workspacebuilds/$build_id/parameters`
endpoint, requiring a separate API call for every build.
The Tasks dashboard fetches Task workspaces in order to show them in a
list, and then needs to fetch the value of the `AI Prompt` parameter for
every task workspace (using its latest build id), requiring an
additional API call for each list item. This endpoint will allow the
dashboard to make just 2 calls to render the list: one to fetch task
workspaces, the other to fetch prompts.
<img width="1512" alt="Screenshot 2025-06-20 at 11 33 11"
src="https://github.com/user-attachments/assets/92899999-e922-44c5-8325-b4b23a0d2bff"
/>
Related to https://github.com/coder/internal/issues/660.
Mathias Fredriksson