fix: use venv and auto-detect Python 3.9+ in install.sh

[arunpamulapati]

• Auto-detect Python 3.9+ from available interpreters
• Create virtual environment to avoid PEP 668 restrictions on newer Python
• Fix shebang from #/bin/bash to #!/bin/bash
• Use consistent Python command throughout the script

Description

Type of Change

• [ X] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (non-code changes like README or docs)

How Has This Been Tested?

Checklist

• I have reviewed the CONTRIBUTING and VERSIONING documentation.
• My code follows the code style of this project.
• I have verified, added or updated the tests to cover my changes (if applicable).
• I have verified that my changes do not introduce any breaking changes on all the supported clouds (AWS, Azure, GCP).
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (if applicable).

Screenshots (If Applicable)

Additional Notes