Transaction Manager: configurable `increaseGasPrice` behavior

Previously, the gas price in the transaction manager would use the generated estimate always, in a function called `increaseGasPrices`.

In [this PR ](https://github.com/ethereum-optimism/optimism/pull/12169#pullrequestreview-2334633109), it's being modified such that if the incoming transaction is already priced higher than the estimate, the higher value is always used.

This behavior is probably fine, but there may be customers who prefer (or even rely on) the limit going back down.

We should add into the configuration for SimpleTransactionManager, some way to specify the behavior, likely a simple flag.

Start with SimpleTransactionManager configuration and the increaseGasPrices behavior described in the issue. Determine how the configuration should select whether an incoming transaction's higher gas price is retained or allowed to fall back to the generated estimate; done means both behaviors are configurable and covered by the relevant tests.

Written by the indexing model from the issue text.