Fix duplicate -c click option parameter conflict

[eshaanag]

Fixes #5265

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)

Description

This PR resolves the UserWarning: The parameter -c is used more than once Click error reported in #5265.

The issue was caused by two options registering the same short option -c:

1. --config-file registered with -c in src/scancode/cli.py.
2. --copyright registered with -c in src/cluecode/plugin_copyright.py.

Since -c has historically been the shortcut for --copyright in scancode and is extensively documented, we resolved the conflict by removing the short flag -c from --config-file, leaving it as --config-file.

Changes

• Removed -c short option from the --config-file declaration in src/scancode/cli.py.
• Updated all related help text golden files: help.txt and help_linux.txt.
• Updated the CLI reference and core options documentation snippets.
• Commits are signed off (DCO) and GPG-signed.