Avoid multiple requests DDoS to rpc entpoints (ostracon#672)

[0Tech]

The subject of the triage:

• feat: add max_batch_request_num feature ostracon#672

[loloicci]

Finschia/ostracon#672 adds a request limit to rpc endpoint. This is for avoiding DDoS. But @ulbqb says that it is unnecessary. Finschia/ostracon#649 (comment)

[loloicci]

Now, MaxBodyBytes is enough big value to contain a contract in Finschia. So we need this limit to avoid DDoS.

[loloicci]

We can suggest it to upstream.