Prepare to release 0.21.0

[lidongze0629]

🤖 Generated by Copilot at a840013

Use updated graphscope-dev image and build wheels for Python 3.7 in k8s/internal/Makefile. This simplifies the installation process and supports a newer Python version.

What do these changes do?

🤖 Generated by Copilot at a840013

• Change the docker image tag for graphscope-dev from vineyard version to wheel to use the latest image with pre-built wheels for graphscope and graphscope-client (link, link, link)
• Add Python 3.7 support for graphscope-client by building the wheel for cp37-cp37m in the Makefile (link)

Related issue number

Fixes

[codecov-commenter]

Codecov Report

Merging #2637 (a840013) into main (2adb251) will decrease coverage by 31.54%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2637       +/-   ##
===========================================
- Coverage   72.96%   41.43%   -31.54%     
===========================================
  Files          99       99               
  Lines       10279    10279               
===========================================
- Hits         7500     4259     -3241     
- Misses       2779     6020     +3241     

see 51 files with indirect coverage changes

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