Revisit pipeline tree load

[evidolob]

Now when user open pipeline tree we first create root tree items, for each of them load child and only after that we show root items in the tree.
We trying to use cache for all tekton tree items, but, for some reasons we put in the cache Pipeline nodes but never get them from cache.

I think that showing tekton tree and root items fast and than load only nodes that user wants to open(on tree item expand) will be much better UX than current implementation when we have a long load period for root items and then again we re load Pipeline nodes. Such behavior can be a problem on slow internet connection or when we have big set of different tekton objects in a cluster.

So I propose next:

• rework tekton tree to lazy load for all nodes, without pre-cache
• use cache for some requests, like getting taskruns
• Improve tekton tree refresh Improve tekton tree refresh  #239