feat: Find OpenAPI client generator for dart

[gawi151]

Is your feature request related to a problem? Please describe. Generate dart api client from OpenAPI spec.

Describe the solution you'd like Tool that will generate most of the code for our client. Ideally should support Dart 3 + OpenAPI 3.1

[gawi151]

So in the process of looking for open api generator I looked at:

• https://github.com/OpenAPITools/openapi-generator
• https://github.com/tazatechnology/openapi_spec

As a result of the research I decided to go with:

• https://github.com/tazatechnology/openapi_spec

Why:

• the openapi-generator has 2 types of Dart generators and both are quite dated
  • It's pure dart generator is using old Dart 2 (not too much support for modern dart 3)
  • dio + built_value generator is quite verbose when creating objects for API request - checkout built_value example
  • generator itself is written in Java
  • generator is not supporting OpenAPI 3.1 too well (a lot of issues in the repo + dart generators are much more behind than more popular languages generators)
• openapi_spec is much newer
  • Written in Dart - easier to modify it for Flutter/Dart developer
  • Also, doesn't support OpenAPI 3.1 well but it's easier to add required support. I created a fork so our code generation can use it
  • uses freezed under the hood to create models (it's much more common nowadays than built_value)