torchrec support on kvzch ebc emb lookup module (#3106)

Summary:
Pull Request resolved: #3106

# Change logs
1. add ZeroCollisionKeyValueEmbeddingBag emb lookup
2. address existing unit test missing for ebc ssd offloading
3. add new ut for kv zch embedding bag module

Embedding bag update is same as embedding update. Details can be found in D73567631

Reviewed By: duduyi2013, kausv

Differential Revision: D76636927

fbshipit-source-id: b273bbe902e571d1f611c10ad3a218ad12db1633

Author: EddyLXJ