feat: dvc stage list --json

[sjawhar]

Adds a dvc stage list --json flag, for machine-readable output. I'd like to use this as a replacement for the dvc repro --dry hack that I implemented in the VS Code extension

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

[codecov]

Codecov Report

❌ Patch coverage is 98.76543% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.03%. Comparing base (2431ec6) to head (b597645).
⚠️ Report is 175 commits behind head on main.

Files with missing lines	Patch %	Lines
dvc/commands/stage.py	91.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10944      +/-   ##
==========================================
+ Coverage   90.68%   91.03%   +0.35%     
==========================================
  Files         504      507       +3     
  Lines       39795    41182    +1387     
  Branches     3141     3255     +114     
==========================================
+ Hits        36087    37490    +1403     
- Misses       3042     3055      +13     
+ Partials      666      637      -29     

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[skshetry]

The title and the description says status --json but the implementation adds stage list --json.

[sjawhar]

The title and the description says status --json but the implementation adds stage list --json.

Sorry