move caffe2/proto/ to its own Bazel package (#97600)
This is just to break up build files and make the system easier to
reason about during the transition to the common build system.
Differential Revision: [D44395826](https://our.internmc.facebook.com/intern/diff/D44395826/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97600
Approved by: https://github.com/PaliC
