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>

.goreleaser.yaml

@@ -58,7 +58,7 @@ builds:
   flags:
   - -trimpath
   ldflags:
-  - -s -w -X gitea.com/gitea/act_runner/cmd.version={{ .Summary }}
+  - -s -w -X gitea.com/gitea/act_runner/internal/pkg/ver.version={{ .Summary }}
   binary: >-
     {{ .ProjectName }}-
     {{- .Version }}-