Support labels value for client API add application endpoint

[khanhtc1202]

What this PR does:

Support labels value for client API - add application endpoint

Why we need it:

User can register applications with label values via PipeCD Web UI, they should be able to do the same using PipeCD cli (pipectl or terraform)

Which issue(s) this PR fixes:

Related PR #6692

Does this PR introduce a user-facing change?:

• How are users affected by this change: Possible to register applications with label values via pipectl
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.48%. Comparing base (60d7269) to head (fcceed9).

Files with missing lines	Patch %	Lines
pkg/app/pipectl/cmd/application/add.go	0.00%	10 Missing ⚠️
pkg/app/server/grpcapi/api.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6724   +/-   ##
=======================================
  Coverage   29.47%   29.48%           
=======================================
  Files         593      593           
  Lines       63440    63451   +11     
=======================================
+ Hits        18702    18706    +4     
- Misses      43292    43300    +8     
+ Partials     1446     1445    -1     

Flag	Coverage Δ
.	23.28% <0.00%> (-0.01%)	⬇️
.-pkg-app-pipedv1-plugin-analysis	32.43% <ø> (ø)
.-pkg-app-pipedv1-plugin-ecs	31.82% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes	58.37% <ø> (ø)
.-pkg-app-pipedv1-plugin-kubernetes_multicluster	61.90% <ø> (ø)
.-pkg-app-pipedv1-plugin-scriptrun	54.83% <ø> (ø)
.-pkg-app-pipedv1-plugin-terraform	37.95% <ø> (ø)
.-pkg-app-pipedv1-plugin-wait	33.04% <ø> (ø)
.-pkg-app-pipedv1-plugin-waitapproval	52.71% <ø> (ø)
.-pkg-plugin-sdk	50.34% <ø> (+0.19%)	⬆️
.-tool-actions-gh-release	19.23% <ø> (ø)
.-tool-actions-plan-preview	25.51% <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.