feat: handle enums automatically

[stuebingerb]

Previously, enums had to be manually added to a schema using enum<Class>(), e.g.

schema {
    enum<FilmType>()
    query("getEnum") {
        resolver { -> FilmType.FULL_LENGTH }
    }
}

This was a non-intuitive source of errors that especially new users were facing.

Now, enums are handled automatically, so the following definition is now valid:

schema {
    query("getEnum") {
        resolver { -> FilmType.FULL_LENGTH }
    }
}

Resolves #253

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.30%. Comparing base (e5df722) to head (1157499).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #408      +/-   ##
==========================================
+ Coverage   77.26%   77.30%   +0.03%     
==========================================
  Files         152      152              
  Lines        4865     4877      +12     
  Branches      843      845       +2     
==========================================
+ Hits         3759     3770      +11     
  Misses        788      788              
- Partials      318      319       +1     

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