Feat: support fallback to kubeconfig namespace when env not set

[wonderflow]

Signed-off-by: Jianbo Sun jianbo.sjb@alibaba-inc.com

Description of your changes

Fixes #5121

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

Base: 61.08% // Head: 61.10% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (b97fd9f) compared to base (e63aa44).
Patch coverage: 45.45% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5182      +/-   ##
==========================================
+ Coverage   61.08%   61.10%   +0.02%     
==========================================
  Files         305      305              
  Lines       45337    45358      +21     
==========================================
+ Hits        27692    27715      +23     
+ Misses      14800    14798       -2     
  Partials     2845     2845              

Flag	Coverage Δ
apiserver-e2etests	35.02% <0.00%> (+0.03%)	⬆️
apiserver-unittests	36.87% <ø> (+0.01%)	⬆️
core-unittests	55.10% <45.45%> (+0.06%)	⬆️
e2e-multicluster-test	18.91% <0.00%> (-0.05%)	⬇️
e2e-rollout-tests	20.53% <0.00%> (-0.05%)	⬇️
e2etests	25.97% <0.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
pkg/utils/common/args.go	34.21% <42.85%> (+1.95%)	⬆️
pkg/oam/util/helper.go	64.00% <100.00%> (ø)
pkg/apiserver/event/sync/cr2ux.go	45.88% <0.00%> (-4.71%)	⬇️
...es/policydefinition/policydefinition_controller.go	69.51% <0.00%> (-3.66%)	⬇️
pkg/resourcekeeper/gc.go	77.97% <0.00%> (-2.09%)	⬇️
pkg/velaql/providers/query/collector.go	68.80% <0.00%> (-1.84%)	⬇️
...dev/v1alpha2/application/application_controller.go	84.97% <0.00%> (-1.18%)	⬇️
pkg/velaql/providers/query/tree.go	85.27% <0.00%> (-0.40%)	⬇️
pkg/addon/registry.go	51.26% <0.00%> (ø)
pkg/multicluster/virtual_cluster.go	77.28% <0.00%> (+0.36%)	⬆️
... and 7 more

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