Put API/networking errors on another error code

[another-rex]

Separate out API errors into its own error code. The intention is to avoid lumping everything in error 127, since it is reserved for general errors not actionable by the user.

Errors related to the API should be separate as they are actionable by the user (e.g. the CI it's running on has no access to the internet), or our API is timing out, so they should try again...etc.

Another motivation is that currently because API errors are mixed in with general errors, it's not clear to the user what caused the osv-scanner GitHub action to fail, since we specifically ignore general errors and set the exit code to 0 in the GitHub action, as this could be caused by failing to parse a specific lockfile. This leads to situations like: https://github.com/google/osv.dev/actions/runs/8243615203/job/22544495994?pr=2048 , where it's unclear what the actual error is (it is hiding under Run Scanner For Existing Code step, which is a check).

This PR also clarifies the error wording to make it clear which query caused the error.

TODO: (In followup PRs)

• Guided Remediation
• Automated updates

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 61.16%. Comparing base (b28c1c8) to head (4ca052c).
Report is 26 commits behind head on main.

Files	Patch %	Lines
pkg/osvscanner/osvscanner.go	0.00%	4 Missing ⚠️
cmd/osv-scanner/main.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #857      +/-   ##
==========================================
+ Coverage   59.78%   61.16%   +1.37%     
==========================================
  Files         136      144       +8     
  Lines       11268    11807     +539     
==========================================
+ Hits         6737     7222     +485     
- Misses       4102     4112      +10     
- Partials      429      473      +44     

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