Persist and load the start time of wait stage to deal with restart case

[nghialv]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #125

Does this PR introduce a user-facing change?:

NONE

[nghialv]

/cc @nakabonne

[pipecd-bot]

The following files are not gofmt-ed. By commenting /golinter fmt, the formatted one will be appended to this pull request automatically.

pkg/app/piped/executor/wait/wait.go

--- pkg/app/piped/executor/wait/wait.go.orig
+++ pkg/app/piped/executor/wait/wait.go
@@ -20,9 +20,10 @@
 	"strconv"
 	"time"
 
+	"go.uber.org/zap"
+
 	"github.com/pipe-cd/pipe/pkg/app/piped/executor"
 	"github.com/pipe-cd/pipe/pkg/model"
-	"go.uber.org/zap"
 )
 
 const (

[pipecd-bot]

Code coverage for golang is 24.23%. This pull request decreases coverage by -0.13%.

File	Function	Base	Head	Diff
pkg/app/piped/executor/wait/wait.go	Executor.retrieveStartTime	--	0.00%	+0.00%
pkg/app/piped/executor/wait/wait.go	Executor.saveStartTime	--	0.00%	+0.00%
pkg/app/piped/executor/wait/wait.go	Executor.Execute	0.00%	0.00%	+0.00%

[nghialv]

/golinter fmt

[pipecd-bot]

Code coverage for golang is 24.23%. This pull request decreases coverage by -0.13%.

File	Function	Base	Head	Diff
pkg/app/piped/executor/wait/wait.go	Executor.retrieveStartTime	--	0.00%	+0.00%
pkg/app/piped/executor/wait/wait.go	Executor.saveStartTime	--	0.00%	+0.00%
pkg/app/piped/executor/wait/wait.go	Executor.Execute	0.00%	0.00%	+0.00%

[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.