[Improvement][Spark] Provide APIs for data transformation at the graph level

[lixueclaire]

Proposed changes

This change adds a GraphTransformer for the data transformation at the graph level. The methods can help the users to transform graphs through specifying yaml paths or GraphInfo objects of the two graphs.

Types of changes

What types of changes does your code introduce to GraphAr?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

related to issue #88

[github-actions]

🎊 PR Preview 5ee8447 has been successfully built and deployed to https://alibaba-graphar-build-pr-113.surge.sh

_{🤖 By surge-preview}

[acezen]

LGTM~