[PAN-2850] Create a transaction pool configuration object

[AbdelStark]

PR description

Regroup txPoolMaxSize, pendingTxRetentionPeriod, txMessageKeepAliveSeconds CLI options into one TransactionPoolConfiguration object.

Fixed Issue(s)

[mbaxter]

(Discussion) What about folding minTransactionGasPrice into TransactionPoolConfiguration? Or maybe the TransactionPool also gets access to MiningParams so that we don't end up duplicating data on 2 different config objects?

[AbdelStark]

Yes it makes sense.

[AbdelStark]

I mean the second approach where TransactionPool also gets access to MiningParams

[AbdelStark]

Actually the PantheonControllerBuilder passes the minTransactionPrice to the transactionPool from the MiningParams

    final TransactionPool transactionPool =
        TransactionPoolFactory.createTransactionPool(
            protocolSchedule,
            protocolContext,
            ethProtocolManager.ethContext(),
            clock,
            metricsSystem,
            syncState,
            miningParameters.getMinTransactionGasPrice(),
            transactionPoolConfiguration)

SInce it uses only one parameter from the MiningParams i don't think we need to give it access to the whole object now. What do you think ?

[mbaxter]

🤷‍♀ Just feels odd to have a config object and then have an additional dangling option. But there's some weirdness with all 3 options really (as is + my 2 alternative suggestions). I think I'm leaning towards passing in the MiningParams - it makes it more explicit that the transactionPool's behavior is modified by the mining configuration. But I'll leave it up to you.