feat: add export task for OpenGalaxy with ngraph

[frank-zsy]

close #1208

This PR contains a new task to export OpenGalaxy data by month from Neo4j database.

The task process should be able to:

• Export whole GitHub user-repo activity network data by month.
• Export data with format that can be used be OpenGalaxy now.
• Support continuous 3d layout in timeline.
• Export OpenDigger repo label data at same time.

[frank-zsy]

I will reduce the iterations from 3,000 to 1,000 times since continuous 3d layout supported. Which means the initial position of each repo and user node will be derived from last month, so we don't really need that a lot iterations to meet the stable state.