Update k8s executor to follow specified routes when applying manifests

[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. Add test for this applierGroup function.

pipecd/pkg/app/piped/executor/kubernetes/applier_group.go

Lines 70 to 73 in 3597e07

	// TODO: Add test for this applierGroup function.
	func (d applierGroup) Get(rk provider.ResourceKey) (provider.Applier, error) {
	for _, r := range d.resourceRoutes {
	if r.Match == nil {

This was created by todo plugin since "TODO:" was found in 3597e07 when #3817 was merged. cc: @nghialv.

[khanhtc1202]

Here you go