Update web API to return the real data of application counts

[nghialv]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

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. Cache application counts in the cache service.

https://github.com/pipe-cd/pipe/blob/0c4ff7e5dbbca3abd0ff190933aec4b7cdc32c5a/pkg/app/api/grpcapi/web_api.go#L1465-L1468

This was created by todo plugin since "TODO:" was found in 0c4ff7e when #1990 was merged. cc: @nghialv.

[pipecd-bot]

Code coverage for golang is 32.93%. This pull request increases coverage by 0.07%.

File	Function	Base	Head	Diff
pkg/app/api/grpcapi/web_api.go	WebAPI.GetInsightApplicationCount	0.00%	0.00%	+0.00%
pkg/app/ops/insightcollector/applications.go	Collector.updateApplicationCounts	0.00%	0.00%	+0.00%
pkg/insight/applicationcount.go	MakeApplicationCounts	0.00%	100.00%	+100.00%

[khanhtc1202]

🚀
/lgtm

[nakabonne]

🤒
/approve

[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.