Feat: add mode in steps for step group

[FogDong]

Description of your changes

Feat: add mode in steps for step group

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Special notes for your reviewer

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.03 ⚠️

Comparison is base (c730c05) 67.48% compared to head (19df50f) 67.45%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #153      +/-   ##
==========================================
- Coverage   67.48%   67.45%   -0.03%     
==========================================
  Files          49       49              
  Lines        4505     4507       +2     
==========================================
  Hits         3040     3040              
- Misses       1071     1072       +1     
- Partials      394      395       +1     

Flag	Coverage Δ
e2etests	22.77% <0.00%> (-0.02%)	⬇️
unit-test	64.39% <0.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
api/v1alpha1/types.go	11.11% <ø> (ø)
pkg/generator/generator.go	67.71% <0.00%> (-1.09%)	⬇️

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[FogDong]

/backport 0.5

[github-actions]

Successfully created backport PR #154 for release-0.5.