Use graphql Guard to remove auth checks from resolvers

[tpoliaw]

Using the attributes allows the auth logic to be separated from the
logic in the resolver endpoints and makes it easier to re-use the checks
for other future endpoints if they're added.

[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.58%. Comparing base (dd725e6) to head (1d139a2).

Files with missing lines	Patch %	Lines
src/graphql/auth.rs	76.19%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   77.52%   77.58%   +0.05%     
==========================================
  Files          13       13              
  Lines        1909     1905       -4     
==========================================
- Hits         1480     1478       -2     
+ Misses        429      427       -2     

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