fix: Allow enum -> String conversion in GraphQL schema validator

[ferenc-csaky]

Key Changes

• Generate GraphQL schema for temporal-join use-case, and add Placements enum and field
• Add placement field to the mutation table in the SQRL script
• Adapt tests and snapshots

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.10%. Comparing base (eb0726a) to head (01bb0c3).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...a/com/datasqrl/graphql/GraphqlSchemaValidator.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2002      +/-   ##
============================================
- Coverage     13.10%   13.10%   -0.01%     
  Complexity      780      780              
============================================
  Files           595      595              
  Lines         16861    16862       +1     
  Branches       1972     1973       +1     
============================================
  Hits           2210     2210              
- Misses        14448    14449       +1     
  Partials        203      203              

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