Improve install.sh

[clairem-sl]

Description

Two issues with the current install.sh for Linux:

1. The die and warn functions chop the string to only its first word
2. There is no way to skip the backup step; doing backup using mv results in failure if the installation directory is mounted on a separate filesystem.

This PR provides 2 things:

1. Fixing the output of error message
2. Option to skip backup

Related Issues

No related issue that I know of.

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Checklist

Please ensure the following before requesting review:

• I have provided a clear title and detailed description for this pull request.
• If useful, I have included media such as screenshots and video to show off my changes.
• I have tested the changes locally and verified they work as intended.
• All new and existing tests pass.
• Code follows the project's style guidelines.
• Documentation has been updated if needed.
• Any dependent changes have been merged and published in downstream modules
• I have reviewed the contributing guidelines.

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Additional Notes

Skipping of backup process is done like so:

NOBACKUP=1 ./install.sh

or if installing using sudo:

NOBACKUP=1 sudo --preserve-env=NOBACKUP ./install.sh