Calculate ForgeBatch gasLimit with parametrized formula

Add the following config parameters at
`Coordinator.EthClient.ForgeBatchGasCost`:
- `Fixed`
- `L1UserTx`
- `L1CoordTx`
- `L2Tx`
Which are the costs associated to a ForgeBatch transaction, split
into different parts to be used in the formula to compute the gasLimit.

node/node.go

@@ -336,6 +336,7 @@ func NewNode(mode Mode, cfg *config.Node) (*Node, error) {
 					PurgeBlockDelay:      cfg.Coordinator.L2DB.PurgeBlockDelay,
 					InvalidateBlockDelay: cfg.Coordinator.L2DB.InvalidateBlockDelay,
 				},
+				ForgeBatchGasCost: cfg.Coordinator.EthClient.ForgeBatchGasCost,
 				VerifierIdx:       uint8(verifierIdx),
 				TxProcessorConfig: txProcessorCfg,
 			},