Enhance macOS compatibility in installation script

- Added checks to ensure the script is executed, not sourced.
- Improved OS detection and handling for macOS and Linux.
- Updated directory paths for macOS.
- Introduced cross-platform helper functions for downloading files and modifying files.
- Added functionality to patch the .dappnode_profile for macOS compatibility.
- Enhanced user shell configuration to source the profile correctly.
- Cleaned up rc.local for Linux installations.
- Improved logging and user feedback during installation.

Author: pablomendezroyo