Remove setting defaults in the SDK

[Warashi]

What this PR does:

This PR removes the code setting defaults in the SDK.

Why we need it:

It's clear to implement setting default values in the plugin code.

Which issue(s) this PR fixes:

Part of #5530

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):

[khanhtc1202]

It's better to let the dev manage how to set values ​​for plugin config 🙆‍♂️

[ffjlabo]

LGTM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.57%. Comparing base (1a0e3c2) to head (4d787b9).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6168   +/-   ##
=======================================
  Coverage   28.56%   28.57%           
=======================================
  Files         535      535           
  Lines       57288    57285    -3     
=======================================
+ Hits        16364    16367    +3     
+ Misses      39652    39647    -5     
+ Partials     1272     1271    -1     

Flag	Coverage Δ
.	23.13% <ø> (+<0.01%)	⬆️
.-pkg-app-pipedv1-plugin-analysis	62.85% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	60.91% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.48% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	54.83% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	38.31% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-app-pipedv1-plugin-waitapproval	68.62% <ø> (ø)
.-pkg-plugin-sdk	50.32% <ø> (+0.07%)	⬆️
.-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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[t-kikuc]

I added change-category/notable-change since this PR forces existing plugins to modify handling defaults.