[Terraform Plugin] Plan stage

[t-kikuc]

What this PR does:

• Copied terraform/provider from platformprovider/terraform
  • Fixed model.xxx to sdk.xxx
• Created initialize.go and plan.go based on piepdv0 executor (https://github.com/pipe-cd/pipecd/tree/master/pkg/app/piped/executor/terraform)

Why we need it:

To support TERRAFORM_PLAN stage.

Which issue(s) this PR fixes:

Part of #5992

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 30.26634% with 288 lines in your changes missing coverage. Please review.

Project coverage is 28.30%. Comparing base (da6fce4) to head (0363eff).
Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
...app/pipedv1/plugin/terraform/provider/terraform.go	30.62%	177 Missing and 11 partials ⚠️
.../pipedv1/plugin/terraform/deployment/initialize.go	10.52%	51 Missing ⚠️
...kg/app/pipedv1/plugin/terraform/deployment/plan.go	0.00%	25 Missing ⚠️
...kg/app/pipedv1/plugin/terraform/provider/module.go	72.00%	9 Missing and 5 partials ⚠️
.../app/pipedv1/plugin/terraform/deployment/plugin.go	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6006      +/-   ##
==========================================
+ Coverage   28.16%   28.30%   +0.13%     
==========================================
  Files         519      527       +8     
  Lines       55938    56542     +604     
==========================================
+ Hits        15757    16004     +247     
- Misses      38931    39271     +340     
- Partials     1250     1267      +17     

Flag	Coverage Δ
.	23.27% <ø> (+0.04%)	⬆️
.-pkg-app-pipedv1-plugin-kubernetes	65.94% <ø> (-0.33%)	⬇️
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	67.33% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	66.66% <ø> (?)
.-pkg-app-pipedv1-plugin-terraform	38.11% <30.26%> (-42.15%)	⬇️
.-pkg-app-pipedv1-plugin-wait	35.51% <ø> (ø)
.-pkg-plugin-sdk	50.71% <ø> (-0.22%)	⬇️
.-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)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[khanhtc1202]

LGTM with some nits

[khanhtc1202]

Thank you 👍