use index-url instead of extra-index-url for pytorch nightlies

[agunapal]

Description

This PR fixes the torch.compile. nightly benchmark failure.
Issue is resolved by pointing to Pytorch's index instead of Pypi.

Fixes #(issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

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.

• Logs

Starting AB benchmark suite...


Configured execution parameters are:
{'tmp_dir': '/tmp', 'report_location': '/tmp', 'config_properties': './benchmarks/config.properties', 'url': 'https://torchserve.pytorch.org/mar_files/resnet-50-scripted.mar', 'exec_env': 'local', 'gpus': 'all', 'concurrency': 100, 'requests': 10000, 'batch_size': 1, 'batch_delay': 100, 'input': './examples/image_classifier/kitten.jpg', 'content_type': 'application/jpg', 'workers': 4, 'image': '', 'docker_runtime': '', 'backend_profiling': False, 'handler_profiling': False, 'generate_graphs': False, 'inference_model_url': 'predictions/benchmark', 'benchmark_backend': 'ab', 'result_file': '/tmp/benchmark/result.txt', 'metric_log': '/tmp/benchmark/logs/model_metrics.log', 'inference_url': 'http://127.0.0.1:8080', 'management_url': 'http://127.0.0.1:8081', 'config_properties_name': 'config.properties'}


Preparing local execution...
*Terminating any existing Torchserve instance ...
torchserve --stop
TorchServe has stopped.
*Setting up model store...
*Starting local Torchserve instance...
Running: torchserve --start --model-store /tmp/model_store --workflow-store /tmp/wf_store --ts-config /tmp/benchmark/conf/config.properties  > /tmp/benchmark/logs/model_metrics.log
torchserve --start --model-store /tmp/model_store --workflow-store /tmp/wf_store --ts-config /tmp/benchmark/conf/config.properties  > /tmp/benchmark/logs/model_metrics.log
*Testing system health...
{
  "status": "Healthy"
}

*Registering model...
{
  "status": "Model \"benchmark\" Version: 1.0 registered with 4 initial workers"
}



Executing warm-up ...
ab -c 100 -s 300 -n 1000.0 -k -p /tmp/benchmark/input -T  application/jpg http://127.0.0.1:8080/predictions/benchmark > /tmp/benchmark/result.txt
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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?