[Prover] Updates to `ProvingAgent` to work with new `ProvingBroker`

[alexghr]

The existing ProvingAgent should be updated to work with the new ProvingBroker:

• expose new env vars for enabled proof types
• retry sending proofs indefinitely (in case the broker is down)
• read/write inputs/proofs to/from separate storage (see [prover] Handle connection between orchestrator and broker with multiple pending requests #8490)