Add ImageConfig to GenerationConfig and add new FinishReason types.

[shaxaaa]

https://ai.google.dev/api/generate-content#FinishReason has added a couple of new reasons:

• IMAGE_PROHIBITED_CONTENT - Image generation stopped because generated images has other prohibited content.
• IMAGE_OTHER - Image generation stopped because of other miscellaneous issue.
• NO_IMAGE - The model was expected to generate an image, but none was generated.
• IMAGE_RECITATION - Image generation stopped due to recitation.

Added also https://ai.google.dev/api/generate-content#ImageConfig for image generation features to GenerateConfig.

[Plytas]

Thanks!