[Bug] Invalid flutter client generation

[theEvilReaper]

Describe the bug

We use Swagger annotations to document our endpoints and generate a valid Swagger file. Based on these annotations, we can generate a Flutter client. The generated client is pushed into a dedicated repository, which can then be integrated into Flutter projects.

Currently, the client generation process is missing the flutter build option to generate additional code.

Steps to reproduce the bug

1. Open the generated client repository.
2. Check for missing classes that should have been generated by built_value.