feat(site): use new task data model and endpoints (#20431)

Updates the UI to use the new API endpoints for tasks and use its new
data model.

Disclaimer: Since the base data model for tasks changed, we had to do a
quite large refactor and I'm sorry for that 🙏, but you'll notice most of
the changes are to adjust the types.

Closes coder/internal#976

---------

Co-authored-by: Bruno Quaresma <bruno_nonato_quaresma@hotmail.com>

cli/exp_task_status_test.go

@@ -240,6 +240,7 @@ func Test_TaskStatus(t *testing.T) {
   "template_display_name": "",
   "template_icon": "",
   "workspace_id": null,
+  "workspace_name": "",
   "workspace_status": "running",
   "workspace_agent_id": null,
   "workspace_agent_lifecycle": "ready",