[REQ] [dart] generate ready-to use dart blocs/cubits

Created by: ayushin

https://github.com/OpenAPITools/openapi-generator/issues/3785

I believe it would be a great help for the flutter/dart community if openapi-generator could generate the repositories boilerplate for the BLOC design patter as was discussed in the issue above.

I understand that many (including myself) have already done some work/research on the subject, so it would be great to combine the efforts and provide a joint uniform solution for this.