[K8s plugin] Delete baseline/canary variant resources on K8S_ROLLBACK stage

[Warashi]

What this PR does:

as title

Why we need it:

It's supported in pipedv0, so we want to support it in the plugin, also.

Which issue(s) this PR fixes:

Part of #5764

Does this PR introduce a user-facing change?: No

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

[codecov]

Codecov Report

Attention: Patch coverage is 57.69231% with 11 lines in your changes missing coverage. Please review.

Project coverage is 28.46%. Comparing base (fbb422d) to head (163e523).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...p/pipedv1/plugin/kubernetes/deployment/rollback.go	57.69%	8 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5919      +/-   ##
==========================================
+ Coverage   28.42%   28.46%   +0.04%     
==========================================
  Files         520      520              
  Lines       56381    56405      +24     
==========================================
+ Hits        16024    16058      +34     
+ Misses      39093    39081      -12     
- Partials     1264     1266       +2     

Flag	Coverage Δ
.	23.74% <ø> (ø)
.-pkg-app-pipedv1-plugin-example	0.00% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	66.42% <57.69%> (+0.62%)	⬆️
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.51% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	49.33% <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