add debug flag that retains temporary files

[theganyo]

Fixes #1130

[codecov]

Codecov Report

Merging #1166 (10a167d) into main (2d8c94b) will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main    #1166      +/-   ##
==========================================
- Coverage   70.80%   70.79%   -0.02%     
==========================================
  Files         146      146              
  Lines       12048    12054       +6     
==========================================
+ Hits         8531     8534       +3     
- Misses       2796     2797       +1     
- Partials      721      723       +2     

Impacted Files	Coverage Δ
cmd/registry/cmd/compute/lint/lint.go	71.76% <66.66%> (-1.66%)	⬇️

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[theganyo]

FYI: #1130 suggested changing LinterRequest to include a debug flag, but I didn't see any reason to do so for this as the behavior to remove the directory exists at the level of the caller of LinterRequest.