Add an option to not generate for every build

[vsct-jburet]

When I run gradle build, the model and client files are regenerated. Since I will commit the generated code to Git anyway, so I would prefer not to regenerate it every time. My OpenAPI file is quite large.

Moreover, to work around #3 , I currently have to manually modify the generated code anyway.

[dshatz]

Hi!

Currently the code is regenerated if either the API spec or output (generated code) changes or is deleted.

Since you are manually editing the generated code, the Gradle output is invalidated. Can you confirm that if you don't modify the output, it still regenerates on every run?

[vsct-jburet]

In that case, it seems to not be generated on every run. But than it is not doable to manually modify the code :(