Custom Extractor pretrained-foundation-model-v1.2-2024-05-10 and pretrained-foundation-model-v1.3-2024-08-31 are now Stable versions

## Feature Custom Extractor [pretrained-foundation-model-v1.2-2024-05-10](https://cloud.google.com/document-ai/docs/processors-list#processor%5Fcde) and [pretrained-foundation-model-v1.3-2024-08-31](https://cloud.google.com/document-ai/docs/processors-list#processor%5Fcde) are now Stable versions. v1.2 and v1.3 now have the following features: * Fine-tuning is now available in Public preview. * They were internally upgraded to a higher quality model. * The labeling system has been upgraded to use the latest version of the OCR model. v1.2 is recommended for the best quality. v1.3 is recommended for the lowest latency. We recommend creating a new processor and relabeling the training and evaluation documents to benefit from both the improved quality with the new processor versions of Custom Extractor (v1.2 and v1.3) and the enhanced labeling system.