[Enhancement] enhance the rest predict API to put all logic behind transport call

[jngz-es]

Description

Recently we got a security test case failure for testPredictWithReadOnlyMLAccess that is caused by the pr #3597. Basically we have model index reading before transport call in which there is a cluster permission control. So in that test case, we failed to hit the no permission error instead we got an index reading error. This is not correct, we should check the permission at the beginning.

Solution

Move model index reading from rest layer to transport layer.