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 89.76%. Comparing base (0baef34) to head (ae3b6ae).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2922   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files         187      187           
  Lines        9149     9149           
  Branches     1885     1885           
=======================================
  Hits         8213     8213           
  Misses        936      936           

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