feat: add logout command

[Sypher845]

Description

Adds a harbor logout command for better UX, gives users a simple, discoverable way to remove their current credentials from the local config, mirroring the standard login / logout pairing found in CLI tools. Includes a confirmation prompt with -y flag.

• Fixes [feature]: logout command #1019

Command

• harbor logout

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation update
• Chore / maintenance

[codecov]

Codecov Report

❌ Patch coverage is 32.50000% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 9.40%. Comparing base (60ad0bd) to head (9222592).
⚠️ Report is 188 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/harbor/root/logout.go	27.02%	26 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             main   #1016      +/-   ##
=========================================
- Coverage   10.99%   9.40%   -1.59%     
=========================================
  Files         173     322     +149     
  Lines        8671   16122    +7451     
=========================================
+ Hits          953    1516     +563     
- Misses       7612   14471    +6859     
- Partials      106     135      +29     

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