Refactoring schema handling and code generation

[ksysoev]

I'm planning to refactor how currently I'm handling generating types for API schema, and probably as a consequence code generation may need some adjustments as well. Problems I want to solve:

• Schema code generates tons of documentation and it makes unusable go doc for Deriv-api package. I think it better to move schema generated code to separate package to keep documentation more clean.
• Want to try to update to new version of gojsonschema, it used to have problems with AdditionalFields property. Lets see how it works now
• After schema will be moved to separate package, code generation will need some adjustments as well.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.89% 🎉

Comparison is base (89f8fed) 91.36% compared to head (8aef1be) 92.26%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #2      +/-   ##
==========================================
+ Coverage   91.36%   92.26%   +0.89%     
==========================================
  Files           3        3              
  Lines         336      336              
==========================================
+ Hits          307      310       +3     
+ Misses         21       19       -2     
+ Partials        8        7       -1     

Files Changed	Coverage Δ
subscriptions.go	89.18% <ø> (ø)
api.go	93.39% <100.00%> (+1.41%)	⬆️

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