[ADD] installscript: implement Python virtual environment for package…

[davidmonterocrespo24]

This pull request refactors the Odoo installation script to use a Python virtual environment for all Python package installations, improving isolation and compatibility, especially for Ubuntu 24.04 and later. It removes the custom pip_install helper and updates startup and service scripts to launch Odoo using the virtual environment's Python interpreter.

Python environment and package management:

• Introduced a dedicated Python virtual environment at OE_VENV and updated all Python package installations to use this environment, replacing direct system-wide installations. [1] [2] [3]
• Removed the custom pip_install helper function, simplifying package installation logic and avoiding potential issues with system package conflicts. [1] [2]

Startup and service script updates:

• Modified the start.sh script to launch Odoo using the virtual environment's Python interpreter instead of the system Python.
• Updated the service definition to set DAEMON to the virtual environment's Python and adjusted DAEMON_OPTS to include the Odoo binary and config file. [1] [2]