[Misc][WIP]Add benchmark scripts

[Potabk]

What this PR does / why we need it?

The purpose of this PR is to add benchmark scripts for npu, developers can easily run performance tests on their own machines with one line of code .

How to use

Prerequisites

• Please make sure that you have vllm and vllm-ascned installed and npu environment，cause these scripts are specially prepared for npu devices
• To speed up the script， you can download the models and datasets to your local computer in advance and change the path in the json file in the .elastic/nightly-benchmarks/tests folder

Run benchmarks

these scripts can automatically conduct performance testing of serving, through and latency, run the following command:

cd vllm-ascend
bash .elastic/nightly-benchmarks/scripts/run-performance-benchmarks.sh

once the script is finished, you can view the result files in the benchmarks/results folder. and the results may looks like below:

|-- latency_llama8B_tp1.json
|-- serving_llama8B_tp1_sharegpt_qps_1.json
|-- serving_llama8B_tp1_sharegpt_qps_16.json
|-- serving_llama8B_tp1_sharegpt_qps_4.json
|-- serving_llama8B_tp1_sharegpt_qps_inf.json
|-- throughput_llama8B_tp1.json

Does this PR introduce any user-facing change?

How was this patch tested?