op-batcher: Improve throttling controller by also using blob base fee

During a recent batcher incident on OPM and a few other chains, the batcher max. throttled the sequencer because the data backlog grew over the max threshold. However, the growing data backlog wasn't caused by blob congestion but other factors (General Ethereum congestion & base fee hikes) and the blob base fee stayed mostly at 1 wei.

We should consider easing the throttling controller to not throttle as much when there are indications that blob space isn't congested, e.g. when the blob base fee is below a threshold. This avoid overzealous throttling behavior that may unnecessarily impact the chain.