Restrict the request / response payload size of Datapower Gateway's JSON / Binary

"Paload size limitation functionarities in each case(Json/Binary, request/response) uniformaly in datapower gateway. This should not be set each configuration by APIs or products.

ex. JSON/Request:5MB、Json/Response:10MB, Binary/Request:8MB、Binary/Response:20MB

|Collective settings |
| in Datapower Gateway |
|----------------------------|
| payload size limitation |
|----------------------------|
| request | response |
--------|-------------|--------------|
JSON | exit | nothing |
--------|-------------|--------------|
binary | nothing | nothing |
-------------------------------------

Since applications that exposes Web APIs do not control how much payload is sent, the owner of the application can not publish their APIs from the IT infrastructure's protection perspective. As a result, the Collaboratioon of Web API will not be promoted among many companies.
We must protect our application servers from the threat of DoS attack and etc.. , so this improvement is essential as security measures.
Moreover, if some applications endure to some big payloads and a lot of requests, the other application's APIs responses would be very slow because Datapower gateway's latency is going to be worse totally.
Although after v5.0.8.4 each application may control the payload limitation, we can't make limitaiton and control total loads in Datapower gateway, so it does not contribute stable operation work. "