GraphQL - Better error messages formatting

[Premwoik]

This PR addresses MIM-1569 and solves wrongly formatted messages returned to the user from the webserver.

Proposed changes include:

• Unification of the error messages format.
• Introducing more information to authorization errors.
• Testing produced messages.
• Adding a catch that should handle all unexpected internal errors.

[codecov]

Codecov Report

Merging #3454 (6d971fe) into feature/graphql (f491972) will decrease coverage by 0.01%.
The diff coverage is 95.00%.

@@                 Coverage Diff                 @@
##           feature/graphql    #3454      +/-   ##
===================================================
- Coverage            80.84%   80.83%   -0.02%     
===================================================
  Files                  424      424              
  Lines                32529    32566      +37     
===================================================
+ Hits                 26298    26324      +26     
- Misses                6231     6242      +11     

Impacted Files	Coverage Δ
...ngoose_graphql/mongoose_graphql_cowboy_handler.erl	92.00% <90.90%> (+1.58%)	⬆️
src/mongoose_graphql/mongoose_graphql_errors.erl	90.62% <96.55%> (+57.29%)	⬆️
src/mongoose_graphql.erl	91.11% <100.00%> (+0.63%)	⬆️
.../mongoose_graphql/mongoose_graphql_permissions.erl	90.47% <100.00%> (+0.73%)	⬆️
src/mod_roster_mnesia.erl	72.72% <0.00%> (-21.22%)	⬇️
src/mongoose_tcp_listener.erl	76.59% <0.00%> (-4.26%)	⬇️
src/global_distrib/mod_global_distrib_receiver.erl	81.11% <0.00%> (-3.34%)	⬇️
src/logger/mongoose_log_filter.erl	78.08% <0.00%> (-1.37%)	⬇️
src/rdbms/mongoose_rdbms.erl	61.75% <0.00%> (-1.20%)	⬇️
src/mod_muc.erl	74.77% <0.00%> (-0.91%)	⬇️
... and 10 more

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[chrzaszcz]

The code looks good, error handling looks improved. I think some possible GraphQL errors are not fully tested - only formatting is checked. I guess it's just difficult to actually trigger all errors by faulty queries?

[chrzaszcz]

Looks good!