gc: add --skip-failed

[dberenbaum]

Closes #5037. Follows up on the great work started by @courentin in #5038. Also related to #9768 (comment).

Example:

$ dvc gc -A --skip-failed
WARNING: This will remove all cache except items used in the workspace and all git commits of the current repo.
Are you sure you want to proceed? [y/n]: y
WARNING: Failed to collect 'workspace', skipping
WARNING: Failed to collect '964799719df645d5104c541410549f702d2a9b5d', skipping
WARNING: Failed to collect '9c24c7652c3eb28adaa2caafdff7dfdc21f1e449', skipping
WARNING: Failed to collect '616500724541bcd2f7f89584187b00f838ecf9a9', skipping
No unused 'repo' cache to remove.
No unused 'local' cache to remove.
No unused 'legacy' cache to remove.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (77b451d) 90.63% compared to head (78b02b8) 90.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10155      +/-   ##
==========================================
- Coverage   90.63%   90.40%   -0.23%     
==========================================
  Files         496      496              
  Lines       37751    37769      +18     
  Branches     5490     5493       +3     
==========================================
- Hits        34215    34145      -70     
- Misses       2900     2967      +67     
- Partials      636      657      +21     

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[Danila89]

It looks like ready to be merged, doesn't it?)