MEP 32 -- Atomic switching for collection alias

Current state: Disccusion completed

ISSUE: https://github.com/milvus-io/milvus/issues/17131

PRs: TODO

Keywords: Collection Alias, Atomic Switching

Released: TODO

Summary

1. As the name indicates, CollectionAlias is an alias to an existing collection.
2. The collection alias can be updated to a new collection.
3. Within RootCoordinator, Proxy, and all the key components, CollectionName and CollectionAlias are equal.
   e.g. MetaTable.GetCollectionByName(collectionName string, ts typeutil.Timestamp) can receive CollectionAlias and return corresponding CollectionInfo.
4. CollectionAlias ∧ CollectionName = ∅ . CollectionAlias cannot collide with existing CollectionNames.
5. When alias are added, droped or altered, all proxy should receive the change in the same timestamp.
6. When alias are added, droped or altered, the operations online should not be affected, i.e. they still use the alias information when the tasks begin to excute.