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>

internal/pkg/config/config.example.yaml

@@ -0,0 +1,42 @@
+# Example configuration file, it's safe to copy this as the default config file without any modification.
+
+log:
+  # The level of logging, can be trace, debug, info, warn, error, fatal
+  level: info
+
+runner:
+  # Where to store the registration result.
+  file: .runner
+  # Execute how many tasks concurrently at the same time.
+  capacity: 1
+  # Extra environment variables to run jobs.
+  envs:
+    A_TEST_ENV_NAME_1: a_test_env_value_1
+    A_TEST_ENV_NAME_2: a_test_env_value_2
+  # Extra environment variables to run jobs from a file.
+  # It will be ignored if it's empty or the file doesn't exist.
+  env_file: .env
+  # The timeout for a job to be finished.
+  # Please note that the Gitea instance also has a timeout (3h by default) for the job.
+  # So the job could be stopped by the Gitea instance if it's timeout is shorter than this.
+  timeout: 3h
+  # Whether skip verifying the TLS certificate of the Gitea instance.
+  insecure: false
+
+cache:
+  # Enable cache server to use actions/cache.
+  enabled: true
+  # The directory to store the cache data.
+  # If it's empty, the cache data will be stored in $HOME/.cache/actcache.
+  dir: ""
+  # The host of the cache server.
+  # It's not for the address to listen, but the address to connect from job containers.
+  # So 0.0.0.0 is a bad choice, leave it empty to detect automatically.
+  host: ""
+  # The port of the cache server.
+  # 0 means to use a random available port.
+  port: 0
+
+container:
+  # Which network to use for the job containers. Could be bridge, host, none, or the name of a custom network.
+  network_mode: bridge