Fix: Improve pip install reliability lf-act-venv

Fix: Improve pip install reliability lf-act-venv

Enhance the lf-activate-venv function with robust error handling for
pip installations. Add trusted host configurations, proxy detection,
and fallback strategies to address common "Could not find a version"
errors caused by SSL certificate issues, firewall restrictions, and
network connectivity problems in CI/CD environments.

Changes include:
- Added trusted host flags for PyPI mirrors
- Implemented proxy detection and configuration
- Created fallback installation with verbose debugging
- Added individual package installation as final fallback
- Improved error messages with actionable troubleshooting guidance

Change-Id: Ice9471c0bbd4bda471259f7345298de7ce61b9a3
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>