Update default handlers to support batching

[lxning]

🐛 Describe the bug

The existing default handlers are not able to handle batching. Eg.

https://github.com/pytorch/serve/blob/master/ts/torch_handler/text_classifier.py#L49

The correct way should be sth like this.

Error logs

The error log example "number of batch response mismatched, expect: 3, got: 1."

Installation instructions

yes

Model Packaing

ref : same issue #

config.properties

No response

Versions

v0.7.1

Repro instructions

ref : same issue #2119

Possible Solution

No response