The Pool db models accepts "-1" to specify unlimited slots on a pool.
If we currently try to do that on the API side, it will error and result in a 500.
This issue is to fix this behavior so the API can actually serialize and return pools with -1/infinity specified as slots. (same for create and patch).
Then when the backend returns -1 or infinity for those slots, update the UI to take it into account in the chats. (PoolSummary, PoolBar). (infinity should take over the graph)