Refactor to new framework (#98)

- Adjust directory structure
```text
├── internal
│   ├── app
│   │   ├── artifactcache
│   │   ├── cmd
│   │   ├── poll
│   │   └── run
│   └── pkg
│       ├── client
│       ├── config
│       ├── envcheck
│       ├── labels
│       ├── report
│       └── ver
└── main.go
```
- New pkg `labels` to parse label
- New pkg `report` to report logs to Gitea
- Remove pkg `engine`, use `envcheck` to check if docker running.
- Rewrite `runtime` to `run`
- Rewrite `poller` to `poll`
- Simplify some code and remove what's useless.

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/98
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Jason Song <i@wolfogre.com>
Co-committed-by: Jason Song <i@wolfogre.com>

main.go

@@ -5,33 +5,15 @@ package main
 
 import (
 	"context"
-	"os"
 	"os/signal"
 	"syscall"
 
-	"gitea.com/gitea/act_runner/cmd"
+	"gitea.com/gitea/act_runner/internal/app/cmd"
 )
 
-func withContextFunc(ctx context.Context, f func()) context.Context {
-	ctx, cancel := context.WithCancel(ctx)
-	go func() {
-		c := make(chan os.Signal, 1)
-		signal.Notify(c, syscall.SIGINT, syscall.SIGTERM)
-		defer signal.Stop(c)
-
-		select {
-		case <-ctx.Done():
-		case <-c:
-			cancel()
-			f()
-		}
-	}()
-
-	return ctx
-}
-
 func main() {
-	ctx := withContextFunc(context.Background(), func() {})
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
 	// run the command
 	cmd.Execute(ctx)
 }