Add RequestCheckTxAsync channel count as config

[zemyblue]

Summary

Need to add the number of RequestCheckTxAsync channel as config.

Problem Definition

In function NewBaseApp(), the size of the channel is fixed to a magic number of 10000. If there could be more than 10000 requests, the concurrent checkTx would be blocked until some goroutine releases in the channel.

https://github.com/line/lbm-sdk/blob/f7d1830f85c2958fc19ae8e7f8695c566fa1a71d/baseapp/baseapp.go#L143-L157

The number of chCheckTx channel uses magic nubmer 10000.

If the size of chCheckTx is larger than the node mempool size, the node mempool will be full of transaction and could handle any more transactions into the pool;

If the size of chCheckTx is smaller than the node mempool size, it could not make full use of the concurrent checkTx feature as designed to improve the overall performance.

So, need to properly setting the chCheckTx according to the size of mempool from the underlying node.

Proposal

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