[FSDP] Enable mixed hybrid/non-hybrid sharding strategies (#90846)
In the context of hybrid sharding strategies, we only need to enforce the same process groups among the instances using a hybrid sharding strategy, not all instances. We can even mix and match the two different hybrid sharding strategies. This PR relaxes the validation to support this.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90846
Approved by: https://github.com/rohan-varma
