ci: add minimum token permissions for all github workflow files

[opentelemetrybot]

See open-telemetry/sig-security#148 for details.

Please check this PR carefully and watch out for any permission-related workflow failures after merging it.

cc @trask

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.07%. Comparing base (de22600) to head (7e8401d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2922      +/-   ##
==========================================
+ Coverage   89.02%   89.07%   +0.04%     
==========================================
  Files         188      188              
  Lines        9223     9223              
  Branches     1900     1900              
==========================================
+ Hits         8211     8215       +4     
+ Misses       1012     1008       -4     

see 1 file with indirect coverage changes

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