Empower Piped to change how often to sync app config in Git

[nakabonne]

What this PR does / why we need it:
Since an application config file is updated much less frequently than the deployment frequency, the settings should be separated.

Which issue(s) this PR fixes:

Fixes #2809

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. Add doc for appConfigSyncInterval -->

https://github.com/pipe-cd/pipe/blob/4fdc66ba9bff8ce9e650d937c1a1e2acd4bf56e0/docs/content/en/docs-dev/operator-manual/piped/configuration-reference.md#L28-L31

This was created by todo plugin since "TODO:" was found in 4fdc66b when #2833 was merged. cc: @nakabonne.

[khanhtc1202]

Something big has come 😌
/lgtm

[pipecd-bot]

Code coverage for golang is 31.79%. This pull request increases coverage by 0.01%.

File	Function	Base	Head	Diff
pkg/config/config.go	Kind.ToApplicationKind	--	100.00%	+100.00%
pkg/datastore/deploymentchainstore.go	deploymentChainStore.UpdateDeploymentChain	--	0.00%	+0.00%
pkg/app/api/grpcapi/piped_api.go	PipedAPI.CreateDeployment	0.00%	0.00%	+0.00%
pkg/app/piped/appconfigreporter/appconfigreporter.go	Reporter.readApplicationInfo	75.00%	73.33%	-1.67%
pkg/app/piped/trigger/trigger.go	Trigger.checkRepoCandidates	0.00%	0.00%	+0.00%

[pipecd-bot]

This pull request is APPROVED by ono-max.

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.