Implement the traffic routing stage with skeleton code

[Warashi]

What this PR does:

This PR adds executeK8sTrafficRoutingStage implementation with switch-case for traffic routing methods.

Why we need it:

to support traffic routing in k8s plugin

Which issue(s) this PR fixes:

Part of #5764

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Project coverage is 28.19%. Comparing base (69ce763) to head (fef2bb1).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
...pp/pipedv1/plugin/kubernetes/deployment/traffic.go	0.00%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6015      +/-   ##
==========================================
- Coverage   28.21%   28.19%   -0.03%     
==========================================
  Files         520      520              
  Lines       56046    56068      +22     
==========================================
- Hits        15814    15808       -6     
- Misses      38980    39008      +28     
  Partials     1252     1252              

Flag	Coverage Δ
.	23.21% <ø> (-0.02%)	⬇️
.-pkg-app-pipedv1-plugin-kubernetes	65.94% <0.00%> (-0.50%)	⬇️
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.33% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	80.26% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	50.71% <ø> (ø)
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.30% <ø> (ø)
.-tool-codegen-protoc-gen-auth	0.00% <ø> (ø)

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[ffjlabo]

LGTM