Change the spec of sealed secret to provide better visibility in Git

[nghialv]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Part of #749

Does this PR introduce a user-facing change?:

NONE

[pipecd-bot]

The following ISSUES will be created once got merged. If you want me to skip creating the issue, you can use /todo skip command.

Details

---

1. Ensure that the output directory must be inside the application directory.

https://github.com/pipe-cd/pipe/blob/af811cf41ce09b9c0907ba361c38d677240ce1d5/pkg/app/piped/controller/controller.go#L652-L655

This was created by todo plugin since "TODO:" was found in af811cf when #975 was merged. cc: @nghialv.

[pipecd-bot]

Code coverage for golang is 26.62%. This pull request increases coverage by 0.40%.

File	Function	Base	Head	Diff
pkg/config/sealed_secret.go	SealedSecretSpec.RenderOriginalContent	--	92.31%	+92.31%
pkg/app/piped/controller/controller.go	decryptSealedSecrets	0.00%	79.31%	+79.31%

[nakabonne]

👍

[pipecd-bot]

This pull request is APPROVED by nakabonne.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.