Attu-384: refactor for performance

[shanghaikid]

The showCollections api doesn't return lots of useful information, we need to fetch lots api for a single collection, it makes attu unusable if you have a lot collections.

This pr includes:

• use single source of truth in the client side, so that no more fetches all collections between pages
• only update target collection's data if loading or indexing
• only fetch all loaded collections or 5 collections with detail information at most, then the rest of collections will be fetched and sent to the client later by batch with websocket
• bug fixes and code clean

performance result:

• get 40 collections, 2s+ vs 50s+ (tested on milvus v.2.3.10)

This pr should fix #393 and resolve #384 and fix #338