fix: kservev2 batching issue and missing parameters

[pkluska]

Description

Fix KServeV2 picking up only the first item from the list. As a result it is able to dynamically batch the requests. Updated that if the model returns a dictionary it picks up the keys as the names of the outputs.
Update the envelope to handle request parameters and input parameters

Fixes #2158

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Feature/Issue validation/testing

Please describe the Unit or Integration tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• torchserve_sanity.py
  OK

• test_mnist_kf.py

Run completed, parsing output
./ts/torch_handler/unit_tests/test_mnist_kf.py::test_handle Passed

./ts/torch_handler/unit_tests/test_mnist_kf.py::test_handle_kf Passed

./ts/torch_handler/unit_tests/test_mnist_kf.py::test_handle_kfv2 Passed

Total number of tests expected to run: 3
Total number of tests run: 3
Total number of tests passed: 3
Total number of tests failed: 0
Total number of tests failed with errors: 0
Total number of tests skipped: 0
Total number of tests with no result data: 0
Finished running tests!

Checklist:

• Did you have fun?
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?