Hashing in xDS

[ohadvano]

Will appreciate help figuring out if I understand the hashing purpose of xDS correctly. IIUC, the idea of doing this hashing, is to optimize in cases where the remote xDS server may send the same configuration as already exists in Envoy. In that case, by hashing, we're able to guarantee that the config is the same, and skip the work of modifying the underlying resource. Are there other reasons to use hashing for xDS config consumption purposes?

cc @htuch, @adisuissa