Feat: support direct connection mode for cluster gateway

[Somefive]

Description of your changes

If --set multicluster.clusterGateway.direct=true is set, core controller will connect to cluster-gateway directly instead of go to Kubernetes APIServer for delegation.

This has two advantages:

1. The latency of multi-cluster request can be reduced as shown above, 11ms to 6ms. The burden of managed cluster apiserver can be reduced.
2. It does not require hub cluster apiserver and cluster-gateway are mutually connectable. Only require cluster-gateway to be able to connect to hub cluster apiserver.

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: +0.08 🎉

Comparison is base (4596aac) 61.51% compared to head (6f822cc) 61.59%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5595      +/-   ##
==========================================
+ Coverage   61.51%   61.59%   +0.08%     
==========================================
  Files         311      311              
  Lines       48021    48021              
==========================================
+ Hits        29538    29580      +42     
+ Misses      15419    15380      -39     
+ Partials     3064     3061       -3     

Flag	Coverage Δ
apiserver-e2etests	35.78% <ø> (-0.02%)	⬇️
apiserver-unittests	36.35% <ø> (+0.02%)	⬆️
core-unittests	55.72% <ø> (+0.06%)	⬆️
e2e-multicluster-test	19.11% <ø> (+0.12%)	⬆️
e2e-rollout-tests	21.54% <ø> (-0.01%)	⬇️
e2etests	27.13% <ø> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...tepdefinition/workflowstepdefinition_controller.go	77.64% <0.00%> (-3.53%)	⬇️
pkg/apiserver/domain/service/workflow.go	51.95% <0.00%> (-0.36%)	⬇️
pkg/controller/utils/capability.go	81.78% <0.00%> (+0.56%)	⬆️
...dev/v1alpha2/application/application_controller.go	86.59% <0.00%> (+1.13%)	⬆️
pkg/apiserver/domain/service/authentication.go	50.12% <0.00%> (+1.28%)	⬆️
pkg/apiserver/utils/bcode/bcode.go	53.33% <0.00%> (+2.22%)	⬆️
pkg/multicluster/cluster_management.go	39.89% <0.00%> (+2.65%)	⬆️
pkg/auth/kubeconfig.go	52.84% <0.00%> (+3.34%)	⬆️
pkg/apiserver/interfaces/api/oam_application.go	64.28% <0.00%> (+5.10%)	⬆️
...es/policydefinition/policydefinition_controller.go	80.48% <0.00%> (+10.97%)	⬆️

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