Feat: add image pull secret in task step

[Arvintian]

Description of your changes

Fixes #

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

Have run task in my local cluster with private registry.

Special notes for your reviewer

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.70 🎉

Comparison is base (34c6911) 66.85% compared to head (021c79b) 67.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   66.85%   67.56%   +0.70%     
==========================================
  Files          50       50              
  Lines        4547     4547              
==========================================
+ Hits         3040     3072      +32     
+ Misses       1102     1077      -25     
+ Partials      405      398       -7     

Flag	Coverage Δ
e2etests	23.05% <ø> (+0.87%)	⬆️
unit-test	64.27% <ø> (ø)

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see 4 files with indirect coverage changes

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[Somefive]

Let's keep using the same indent.