Upgrade PyTorch to version 2.1.2 and

[davidkyle]

Pytorch was upgraded to 2.1.2 in https://github.com/elastic/ml-cpp/pull/2588 can now be upgraded to the same version.

Models traced in Pytorch 2.1.2 may not be compatible with version 1.13.1 of libtorch used in Elasticsearch 8.12 and earlier. This was the case with an earlier upgrade to Pytorch 1.11 after which #481 was implemented to prevent Eland installing a model into an earlier version of Elasticsearch