Add --skip flag to crosslink tidylist

[jade-guiton-dd]

Integration of crosslink tidylist (cf. #642 for context) in collector-contrib encountered issues, because the output depended on the existence of the cmd/otelcontribcol and cmd/oteltestbedcol, which are autogenerated and gitignored. I had manually filtered them from the output, but their presence still caused changes to the order of the other modules.

This PR introduces a new --skip flag to the crosslink tidylist subcommand, similar to the one on the root command, which specifies go.mod files that should be entirely ignored by the command (omitted from the output, but also ignored when analyzing the dependency graph). Using this in contrib should fix the non-determinism issue.

I also introduced two new tests to help check the determinism of the tool: one checking that the tool defaults to alphabetical order in the absence of dependency constraints, and one checking that --skip works as described above.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.89%. Comparing base (74d4b2b) to head (b9659cd).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #662      +/-   ##
==========================================
+ Coverage   48.86%   48.89%   +0.03%     
==========================================
  Files          57       57              
  Lines        3381     3383       +2     
==========================================
+ Hits         1652     1654       +2     
  Misses       1568     1568              
  Partials      161      161              

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[songy23]

LGTM