Query plan for SPYT engine in QT

[Alexvsalexvsalex]

After having a little discussion we got together on the following. Backend will report query plan as a field spyt_plan in progress yson document.

spyt_plan dict will has two fields:

1. dot - string, represent of graph in dot format.
2. meta - list of strings, info about every node.

HTML template of graph visualization is lying here: https://pastebin.com/ZhU4xVi4
It should be filled and rendered as a new tab Plan in SPYT queries.
All necessary scripts may be found in YTsaurus repository.

Expected result: