Add freezed and reactive form generator support.

[SteveGT96]

Hi grahql_codegen contributors. It's a great job you're making, thanks.
It could be really nice to integreate freezed and reactive_forms_generator, particularly for input types. This could reduce a lot of boilplate code for developpers when dealing with reactive_forms library that is a good choice for form magnagement.

Thanks !

[github-actions]

👋 @SteveGT96
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