[NVIDIA-IMEX] Add test attribute for NVIDIA-imex simulation

[himani2411]

Description of changes

• Add Chef-Attribute to configure Imex-install on any instance
• By dfeault chef keeps the value of this attribute as nil

Tests

• UNIT test
• TEST with PR [SlurmTopo] Add support for slurm Block Topology #3002

DevSettings:
  Cookbook:
    ChefCookbook: https://github.com/himani2411/aws-parallelcluster-cookbook/nvidia-imex-install/tarball
ExtraChefAttributes: |
    {"cluster":{"p6egb200_block_sizes":"1","nvidia":{"imex":{"force_configuration":"true"}}}}

• Contains

ls -al /opt/parallelcluster/shared/nvidia-imex/
total 20
drwxr-xr-x. 2 root root   110 Aug  8 19:32 .
drwxr-xr-x. 5 root root  4096 Aug  8 19:28 ..
-rwxr-xr-x  1 root root 10662 Aug  8 19:32 config_LaunchTemplateA7211c84b953696f.cfg
-rwxr-xr-x  1 root root   129 Aug  8 19:32 nodes_config_LaunchTemplateA7211c84b953696f.cfg

cat /opt/parallelcluster/shared/nvidia-imex/nodes_config_LaunchTemplateA7211c84b953696f.cfg
## Please replace below fake IP's with correct IP address of launched instances in Gb200 Capacity Block
172.31.51.93
172.31.48.43

cat /opt/parallelcluster/shared/nvidia-imex/config_LaunchTemplateA7211c84b953696f.cfg  | grep IMEX_NODE_CONFIG_FILE
IMEX_NODE_CONFIG_FILE=/opt/parallelcluster/shared/nvidia-imex/nodes_config_LaunchTemplateA7211c84b953696f.cfg

systemctl status nvidia-imex
○ nvidia-imex.service - NVIDIA IMEX service
     Loaded: loaded (/etc/systemd/system/nvidia-imex.service; enabled; preset: disabled)
     Active: inactive (dead) since Fri 2025-08-08 19:32:55 UTC; 25min ago
        CPU: 587ms

Aug 08 19:32:55 queue1-st-cr1-1 nvidia-imex[2403]: [Aug 08 2025 19:32:55] [INFO] [tid 2403] Logging file name/path = /var/log/nvidia-imex.log
Aug 08 19:32:55 queue1-st-cr1-1 nvidia-imex[2403]: [Aug 08 2025 19:32:55] [INFO] [tid 2403] Append to log file = 1
Aug 08 19:32:55 queue1-st-c

References

#2996

Checklist

• Make sure you are pointing to the right branch.
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• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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