fix(server): Allow worker tokens to read datasets

[nellh]

Enable worker service tokens to read datasets (currently only writes were allowed).

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.97%. Comparing base (25ee4ad) to head (cdd50fe).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
...ckages/openneuro-server/src/graphql/permissions.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3640      +/-   ##
==========================================
- Coverage   42.97%   42.97%   -0.01%     
==========================================
  Files         635      635              
  Lines       33808    33811       +3     
  Branches     1515     1515              
==========================================
- Hits        14530    14529       -1     
- Misses      19139    19143       +4     
  Partials      139      139              

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